Chapter Nine: How to Think About Truth

For to say of what is that it is not, or of what is not that it is, is false. And to say of what is that it is, and of what is not that it is not, is true.

—Aristotle, Metaphysics

TRUTH, n. An ingenious compound of desirability and appearance.

—Ambrose Bierce, The Devil’s Dictionary

This chapter provides an introduction to one of the central merits of arguments: the truth of premises. In a way, the entire book is about truth, since it aims to offer guidance, by way of good reasoning, for anyone who wishes to know the truth. But the point of this chapter is more specific: it aims to provide detailed practical directions for thinking about whether premises are true.

Remember—it takes only one false premise to render any argument unsound.^[1] A false premise doesn’t guarantee that the conclusion is false, since anyone can concoct a bad argument for a true conclusion. But if the unsound argument is the best reason you have for that conclusion, then it does guarantee that you have no good reason to accept the conclusion as true.

9.1 Objectivity and Truth

9.1.1 Two Laws of Truth

There are two venerable so-called laws of truth which serve us well for practical purposes. One of them, the law of noncontradiction, says that no statement is both true and false. It follows from this that truth is objective and absolute—there cannot be any statement, for example, that is true for you but false for me. Its flip side is the law of the excluded middle, which says that every statement is either true or false. It follows from this that there is no middle ground between the true and the false. Truth-values are evaluations—like true and false—that can be given of how well a statement fits with the world. (In the same way, moral values include evaluations—like good and evil—that can be given of, say, actions; and aesthetic values include evaluations—like beautiful and ugly—that can be given of, say, paintings). Another way of stating the law of the excluded middle is to say there are exactly two truth-values—namely, true and false—with nothing in the middle.

Why, then, is it so commonly asserted that truth is relative, that “what is true for you may be false for me”—a remark that seems to violate the law of noncontradiction? According to one poll, 62 percent of American adults believe that “there is no such thing as absolute truth.” The proportion rises to 74 percent for those ranging in age from 18 to 25.^[2]

Should this be interpreted as flagrant disregard for the law of noncontradiction? Probably not. The survey response provides a good opportunity to apply the principle of charity; these apparent denials of absolute truth are often used as a convenient shorthand for a variety of other related and reasonable expressions, including these:

What you believe to be true I may believe to be false.
What works in your life may not work in mine.
The way you see things may not be the way I see things.
The evidence available to you may not be available to me.
What is reasonable for you may not be reasonable for me.
Neither one of us is in the position to decide the truth for everyone everywhere always.

These paraphrases not only are fully harmonious with the law of noncontradiction, but also are absolutely true.

As Aristotle says, a true statement is one that says of what is that it is and of what is not that it is not. What is may appear to you to be different from the way it appears to me. And you may desire it to be different from the way I desire it to be. But this can’t make what is be two different ways at the same time; it can be only the way it is. When Ambrose Bierce writes satirically of “an ingenious compound of desirability and appearance” it is not really truth that he refers to (and he knows it) but what is often believed to be the truth.

9.1.2 Ambiguity Rather than Relative Truth

Some statements appear to violate these laws even though, on closer inspection, they do not. Consider the following:

Today is July 9.
My name is David Carl Wilson.
A train station is one mile from here.
Chocolate ice cream tastes bad.

When I express these words here and now the statements are true. But when you express them at a different place and time, the statements are probably false. Does this mean they are both true and false or, perhaps, that they are neither?

No. In each case there are two different statements, one true, the other false. We are tempted to think otherwise only because the statements can be referentially ambiguous (to make use of terminology from Chapter 5). When I say today on July 9, it refers to July 9—thus, it can be disambiguated with the true statement Today, July 9, is July 9. But when you say it on November 18, it refers to November 18, and would be properly disambiguated by the false statement Today, November 18, is July 9. My name is David Carl Wilson and A train station is one mile from here are similar. The referents of my and here  would change with a change of speaker and location; when disambiguated, it would become clear that the statement with a different referent is a different statement.

Chocolate ice cream tastes bad is a trickier case. When I say it now it is true, but I probably mean to allow that it could be false when you say it or even when I say it next month. (If I mean instead that it tastes bad always and for everyone—and that you’re just mistaken if you think it tastes good—then I may have a strange view, but there is no apparent lack of objectivity to explain away.) But the statement includes no expression that changes its referent when expressed by a different person or at a different time or in a different place. This is because such an expression is implicit; what I am really saying is Chocolate ice cream tastes bad to me now, which can be made even clearer as Chocolate ice cream tastes bad to David Carl Wilson on July 9.  So when you say it, or when I say it next month, it really is a different statement with potentially a different truth-value. The same thing is usually true of any other sentence including a subjective verb such as tastes, looks, smells, feels, or sounds.

9.1.3 Some Cases in Which You Can’t Decide

I have described the two laws of truth as “useful for practical purposes”—not as necessary, inviolate, and unbending. This is because language is not always law-abiding. The ordinary folks who constantly use language in new and serviceable ways seldom get a note from their logician first. The result is that there are some interesting and puzzling cases in which it is at least conceivable that a statement is both true and false, or that it is neither true nor false. And in each case, there is not any simple and uncontroversial way of settling the matter (though in none of these cases is there any worry about whether truth is objective).

• Robert is bald. (Imagine that Robert is exactly in the border area between bald and not bald.)
• Hans is a Kraut. (Imagine that it is true that Hans is German, but false that Hans is deserving of disparagement on that count.)
• This sentence is false. (Just think about it!)
• Hercules cleaned the Augean stables. (It isn’t clearly true, since Hercules didn’t even exist, but it also seems mistaken to say it is false, since it is certainly truer than, say, Hercules cleaned the Augean stables using power tools.)

Sometimes there is a well-defined fictional world that a character such as Hercules inhabits; in those cases, the best strategy is to evaluate premises like Hercules cleaned the Augean stables according to whether they are true or false in their fictional world. Otherwise, in the fairly unusual instances when statements like these four appear as premises, it is best to evaluate them as can’t decide, with an explanation.

Generally, as we will see, when you evaluate a premise as can’t decide it will be because the evidence you have is more or less evenly balanced; if you were able to collect more evidence, you would be able eventually to settle the question. But it is at least conceivable in these four cases that the reason for evaluating a premise as can’t decide is that there is no fact of the matter—perhaps the statement is neither true nor false, or both true and false, and thus there is no choice to be made regardless of how much evidence you go on to collect. (On this option, indeterminate could actually be a third truth-value, between truth and falsity.) Fortunately, given our practical aims in this text, we don’t need to decide why we can’t decide in these sorts of cases.

9.2 Probability, Evidence, and Truth

What makes a statement true is the way the world is; and it is always possible for me to make a mistake about the way the world is. This is because the world is one thing, while my judgment about the world is something else—and as the ancient proverb says, there is many a slip ‘twixt the cup and the lip. Many things can go wrong in that gap between the world and my judgment about it, no matter how tiny the gap might be. I may have poor evidence. I may be subject to wishful thinking. I may be inattentive. I may be fooled. Thus, it is ordinarily better to avoid evaluating premises with the unmodified adjectives true and false and to prefer expressions such as probably true and probably false (or even, in the strongest cases, certainly true and certainly false, assuming that by this we mean extremes in probability).

9.2.1 Probability as a Measure of Evidence

But what exactly is meant here by probably? There are at least three different and legitimate notions of probability. The one that we are most concerned with in this text is epistemic probability. which is the likelihood that a statement is true, given the total evidence available to you—that is, given all of your background beliefs and experiences. (Epistemic means having to do with knowledge.) This is the notion of probability that should be used in your evaluation of premises. To say in your evaluation that a premise is probably true is just to say that you have fairly good evidence for its truth.

Unlike truth, epistemic probability always comes in degrees. It ranges along a continuum that can be expressed either colloquially (ranging from certainly true to certainly false) or quantitatively (ranging from 1 to 0, respectively). Here are some examples:

Although it can sometimes be useful to express these probabilities quantitatively, doing so is likely to convey a false sense of precision. I might be able to tell the difference between beliefs with epistemic probabilities of .6 and .9 (that is, those that are somewhat probable and those that are very probable), but I doubt that I could discriminate between a .84 and a .85 belief. So I will rely chiefly on the less precise—but less misleading—colloquial expressions.

Epistemic probability, again unlike truth, has a very definite relative component. It is relative to you. It is your evidence—your background beliefs and experiences—that determine whether a statement is epistemically probable for you. There is widespread agreement about epistemic probabilities among many people regarding many statements. This is because we share such a wide range of background beliefs and experiences. Anyone with a rudimentary understanding of U.S. geography, for example, would assign a very high epistemic probability to this statement:

Alaska is larger than Rhode Island.

But consider this statement:

Minnesota is larger than Oregon.

I would have to say that I can’t decide (or that it has an epistemic probability of about .5). My meager evidence does not point clearly in either direction. But there are others (the current governors of the two states, for example, or those who are interested enough to Google it) who have evidence for its truth or falsity which is every bit as strong as the evidence most of us share regarding the statement about Alaska and Rhode Island. For them, it is either almost certainly true or almost certainly false (that is, it has an epistemic probability either close to 1 or close to 0).

It is important to add that epistemic probability has an objective component as well. Given the evidence that you have, there is nothing relative about how probable it makes the premise. There is a fact of the matter about how probable it is—regardless of whether you assess its probability correctly or not. In this way, epistemic probability is like the strike zone in baseball. A pitched ball is in the strike zone if it is over home plate and between the knees and arms of the batter. The strike zone is relative to the batter because a shorter batter or a batter who crouches will have a smaller strike zone. But it also has an objective component. Given the size and stance of the individual batter, there is an objective fact about whether the ball is in the zone—regardless of whether the batter assesses it correctly or not.

9.2.2 Probability as a Measure of Confidence

There is a second notion of probability, one that is not necessarily connected to evidence. Suppose you say, “I’m probably going to win the lottery, even though I realize that everything points against it.” You are acknowledging that the evidence is bad and thus that the epistemic probability of your winning is low. In this case, to say that you will probably win is to say merely that you have confidence you will win. You are not describing the strength of your evidence but the strength of your confidence, that is, the strength of your belief.

This is sometimes termed subjective probability and may be roughly defined as the amount of confidence you have that a given statement is true. Like epistemic probability, it is a matter of degrees and can also be expressed in colloquial terms ranging from certainly true to certainly false or in quantitative terms ranging from 1 to 0. But, unlike epistemic probability, it is relative to you; there is no fact over and above your level of confidence.

If we are intellectually honest—if our aim is to know the truth regarding the questions we care about—then we will endeavor to match subjective probability to epistemic probability. That is to say, we will aim to have the amount of confidence in a statement’s truth that is warranted by the total available evidence. When we succeed, our evaluations of probability will at the same time indicate both epistemic and subjective probability. This frequently does not happen. Even when my evidence for a belief remains the same from today to tomorrow, my mood about it may change. In Chapter 1 much was said about cases in which we adopt and support beliefs with little regard for the evidence—sometimes because of our innocent misuse of shortcuts in reasoning, sometimes because of bad motives. The problem in those cases can now be stated in another way—as the problem of mismatch between the subjective and epistemic probabilities.

The importance of matching subjective with epistemic probability, however, should not tempt you to make certain mistakes. Note, for example, that if I find that my confidence outstrips my apparent evidence—if, for example, I have a hunch that you are a decent human being despite my inability to say exactly why—this is not necessarily an indicator of bad reasoning or dishonesty on my part. It may mean there is some good reason submerged within my total evidence that I have not yet been able to put my finger on—I sense a reason is there, but it isn’t vivid enough for my thinking to have quickly turned it up. Hunches can go in either direction, however—they may be caused by still-subconscious evidence, or they may be caused by wishful thinking. There is no formula for telling the difference; continued cultivation of the intellectual virtues is the only way to get better at doing so.

Another mistake to avoid is the assumption that I must act with tentativeness if my belief is tentative—that is, if my belief is only slightly probable (whether epistemically or subjectively). Consider the statement My child is at the bottom of the pool. If both my evidence and my confidence are only slightly greater than .5 that this is true, it surely does not follow that I should be tentative as I dive in to rescue what may be my child. In short, when it comes to beliefs about the way the world is, confidence about how the belief translates into action must be distinguished from confidence in the belief itself.^[3]

9.2.3 Probability as a Measure of Frequency

There is a third notion of probability—one that occurs often in science, and that differs from the others in that it is entirely objective. Suppose I say, “50 percent of all fair coin tosses come up heads, so there is a .5 probability that this coin toss will come up heads.” I am talking about frequency probability, which may be roughly defined as the likelihood that a specific thing has a property, based on the frequency with which all things of that sort have the property. The probability statement in the example (There is a .5 probability that this coin toss will come up heads) is based on a frequency statement about how frequently fair coin tosses do come up heads (50 percent of all fair coin tosses come up heads).^[4] This is why it is called frequency probability. And because these frequencies are said to occur in the world, independently of our beliefs about them, frequency probability is entirely objective.

Determining the objective facts does involve us subjectively; I try to establish the epistemic probability of a certain frequency probability—that is, I rely on evidence that a certain sort of thing occurs in the world with a certain frequency. But the truth of a typical statement about frequency has nothing to do with whether anyone believes it, has evidence for it, or makes any judgment about it; so this is an entirely objective notion. (Frequency probability is introduced here solely to contrast it with subjective and epistemic probability. We will not need to otherwise refer to it until Chapter 13, when we cover frequency syllogisms.)

9.3 Self-Evidence

Because your evaluations must be expressed in language, you will typically support your beliefs by referring to other beliefs of yours. Recall sample evaluations we have already done. Why do I think, for example, that the sentence Not many people are qualified to work as lifeguards is probably true? Because of another belief of mine—Lifeguards must be in excellent physical shape, must be able to swim well, and must have extensive training. And why do I believe that the sentence If air sacs in birds play a role in their breathing, then carbon monoxide introduced into the air sacs will kill them is probably true? Because of another belief of mine—Carbon monoxide interferes with the ability of blood to carry life-sustaining oxygen.

You are making use of inferential evidence when you support a belief by another belief, since you are saying that you infer one from the other. But you have more than inferential evidence available to you when you consider your evidence. If you had only inferential evidence, then ultimately all of your beliefs would be supported only by one another—and they would together be as well supported as a castle in the clouds. You also have noninferential evidence—that is, you can appeal to something other than your beliefs in support of your beliefs. Noninferential evidence may be divided into two categories: self-evidence and experiential evidence. (Of course, you will be able to express even your non-inferential evidence only as beliefs; but since they are beliefs about self-evidence and experiential evidence, that is enough to bring the castle down out of the clouds and put it on firm ground.)

9.3.1 Self-Evidence and Definition

Suppose you have the easy task of evaluating the following premise:

All bachelors are unmarried.

In most contexts, you do not have to think very hard about why you believe that a premise like this is true. There seems to be no need, for example, to think about what other beliefs lead you to believe this or to look for experiential evidence—to interview bachelors, for example, to find out whether they are married. You can see that it is simply true by definition. Suppose, alternatively, the premise had been this:

Some married men are bachelors.

You might, for similar reasons, say that you can see that it is false by definition.

The evidence we have in these cases is self-evidence, since within the statement itself is found the most important evidence bearing on its truth or falsity—namely, the evidence of the meanings of the words themselves.^[5] A statement that can be seen to be true or false by definition may be described as self-evidently true or false. In self-evidently true or false statements, if you understand what the words mean you ordinarily need no other evidence to make a reasonable decision about truth or falsity.

Shakespeare illustrates this when he has Hamlet tell his friends that he brings “wonderful news,” namely that “there’s ne’er a villain dwelling in all Denmark, but he’s an arrant knave.” Horatio answers, “There needs no ghost, my Lord, come from the grave to tell us this.” In other words, to say that all villains are knaves is self-evidently true to all those who understand the words villain and knave. Self-evidence, however, like all other evidence, is relative to the person; if villain and knave are not included in your vocabulary, Hamlet’s statement will nevertheless be true, but its truth will not be evident to you.

There is much to keep in mind, however, before blithely judging premises to be self-evidently true or false. The term self-evident easily lends itself to abuse; Ambrose Bierce defined it as “evident to one’s self and to no one else.” The point is to avoid using it as another way of saying “it is obvious to me.” Even if something is obvious to you, the purpose of your evaluation is to provide the reasons why it is obvious to you. And only one such reason may be that it is self-evident.

The most famous use of the expression is in the Declaration of Independence: “We hold these truths to be self-evident, that all men are created equal. . . .” But Thomas Jefferson’s use here—while entirely appropriate for that context—is broader than the use recommended for your evaluations. Jefferson might be described as appealing not to definitional but to conversational self-evidence (that is, he appeals to what is evident to ourselves). Jefferson’s conviction that all men are created equal was not based on his understanding of the meanings of terms such as men, created, and equal. His point was that it was evident to all participants in the conversation—to the writers and to the intended audience—that all men are created equal; given this agreement, for the purposes of the conversation there was no need to provide any supporting reasons. This is a perfectly good way to use the expression, but we will use it more narrowly.

Likewise, exercise caution before you judge a premise to be self-evidently false. Consider again the preceding simple example:

Some married men are bachelors.

It would be extremely unusual for someone to make such an obvious mistake. Thus, it provides an especially important opportunity to apply the principle of charity. Is there some clue in the context to suggest, for example, that the arguer is using bachelor or married metaphorically or as shorthand for something else? Maybe the context suggests that the arguer simply means that some married men behave like bachelors. If that proved to be the case, then rather than calling the premise self-evidently false, it would be preferable to paraphrase it charitably and grant that it is almost certainly true—based, perhaps, on your own experience of the behavior of some married men.

This doesn’t mean you will find no self-evidently false statements. The great actor John Barrymore once received a call from the secretary of one of Hollywood’s most important producers. “I am speaking for Mr. Laskin, who wants you to attend an important party he is giving tomorrow,” said the other voice imperiously. “And I,” said Barrymore, “am speaking for John Barrymore, who has a previous engagement which he will make as soon as you have hung up.” There is no problem in understanding Barrymore’s reply to be self-evidently false. The context shows that he meant it to be so, since he clearly meant to return Mr. Laskin’s insult.^[6]

9.3.2 Stipulative Definitions

When we say that a statement is seen to be true by definition, or that it is self-evidently true, we are normally assuming that the words in the statement are being used in a standard way. On some occasions, however, an arguer will decree a nonstandard definition for a term; in such a case, the arguer is using a stipulative definition.

Stipulative definitions can be quite useful. They are sometimes used to add precision to a discussion; in an argument about poverty, the arguer might say, “By poor I mean a family of four that earns less than $12,000 per year.” On other occasions, new words are introduced and defined by stipulation, usually for picking out a notion for which we have no handy term; “By blik,” the philosopher R. M. Hare has said, “I refer to the theoretical framework one uses to interpret the world.”

Premises that stipulate a definition are certainly entitled to be evaluated as self-evidently true, since they are, by stipulation, true by definition. But they do present opportunities for committing the fallacy of equivocation. Suppose after stipulating the preceding definition for poor, I say, “So quit claiming to be poor; you earn almost $13,000 a year for your family.” The conclusion has to do with someone’s real-world concern about being poor; as such, it uses poor in its normal sense, which involves not only yearly earnings but also how many people are supported by the earnings, the other financial resources the family has, and the necessary expenses of the family. But the premise uses it in the more precise, stipulated sense. So the meaning of the term poor has shifted between premise and conclusion, and this means the argument commits the fallacy of equivocation. As described in Chapter 5, the ambiguity should be eliminated in the clarifying process.

A newspaper story seeking to determine the greatest athletes of all time includes the following argument:

Defining athletic greatness as the ability to prove it in at least two highly competitive areas, Babe Ruth was number one. As a pitcher he was a World Series winner, and as a hitter he revolutionized the game. He was the greatest of them all.

One premise of this argument is found in the first sentence, which might be paraphrased as follows:

1. Athletic greatness is to be defined as the ability to prove it in at least two highly competitive areas.

But (skipping the remainder of the argument) the conclusion is this:

Since 1 is a stipulated definition, C is supported only if “greatest athlete” is used there in the same stipulated, nonstandard way as in 1. To avoid equivocation, it should be disambiguated something like this:

Once paraphrased, the question whether he was the greatest athlete (in the standard, non-stipulative sense of the term) remains unanswered by the argument. The argument may now be seen to commit a second argument-based fallacy—the fallacy of missing the point.

9.4 Experiential Evidence

So far we have covered two broad categories of evidence that you will find relevant in putting together the evaluation of a premise. First, there is inferential evidence—that is, other beliefs of yours from which you can infer your evaluation. Second, there is noninferential evidence of a sort that we have termed self-evidence; this is the evidence found in the meanings of terms themselves. But there is another important category that is also noninferential in nature. It is experiential evidence, the evidence provided by sense experience.

9.4.1 What You Have Directly Observed

The most obvious experiential evidence is that which you have observed—what you have seen, heard, smelled, tasted, or touched. Suppose an arguer uses the following premise:

1. All swans are white.

In your evaluation of this premise you might be fully entitled, on the basis of your observations—that is, your sense experience—to say this:

Premise 1 is almost certainly false because I personally saw a black swan at the local zoo.

These sorts of appeals to observation are natural, intuitive, and legitimate. There are, however, three important questions that you should ask when you make such appeals to observation.

The first question is How reliable was your observation, given the circumstances? Perhaps you are not particularly skilled at identifying swans. Or perhaps the lighting was bad, you had a poor viewing angle, you had left your glasses in the car, or the swan had just emerged from the mud. Any of these circumstances would make your observation less than reliable, and if you were aware of the undermining circumstances you should have had less confidence in the observation and, on that basis, should have adjusted the probability in your evaluation.

The second question is How reliable is your memory of the observation? Observations that you appeal to as evidence are ordinarily observations that you remember, not observations that are occurring at that moment. If you just a moment ago made the observation, your memory is probably highly reliable. But you depend on many observations that you made days, weeks, and years ago. Time presents opportunities for memories to fade and to be unconsciously revised—all the more likely if wishful thinking or someone else’s suggestion is prompting you to remember one way rather than another. We are all familiar with this phenomenon, and scientific research has confirmed it. As for the black swan, chances are that your memory is serving you well. But you may have reason to consider it less reliable if I said to you, “After all, it was a couple of years ago. And haven’t you conveniently forgotten that you argued heatedly with me at the time, since I was insisting that it was just an odd-shaped piece of wood protruding from the water?”

The third question is How probable would your belief be had you not made the observation? A slightly more technical way of putting exactly the same thing is to ask what the prior probability of the belief is. (In this case, prior simply means independent of the observation; and it is epistemic probability that is referred to.) The higher the prior probability of the observation, the more reliable it is. Thus, the more likely it is that there is a black swan at the zoo, independent of your having observed it, the more you can trust your observation of it to be reliable. Suppose you read a feature story in the local newspaper that comments on the pride the zoo takes in its collection of five white swans, the only swans it has ever had for the last 10 years. This would significantly reduce the prior probability that there is a black swan and would render your observation somewhat less reliable. It would not mean that you didn’t see one—the news account could have been mistaken, or a black swan may have stopped over for a visit on the day you were there. But it would mean that a single observation has only limited evidential weight.

If someone tells you that a car is coming down the road, you accept it with no question. If someone tells you that several frogs flying on lily pads are coming down the road, you may suggest they take another look. Consider the observations, contained in the following Los Angeles Times account, that some have made on the Willcox Playa, a remote and eerie expanse of desert in southern Arizona:

Most stunning are the Playa’s endless mirages. Everyone sees them. Everyone swears by them—buildings rising from the shimmering horizon, trucks speeding along upside down, groups of people dancing. Pete Cowgill, former outdoor writer for the Arizona Daily Star, once saw a Southern Pacific train chugging across the Playa. As he watched, the engine disappeared into the earth. The next car followed it, then the next, and the next. “One by one, about a hundred cars flat disappeared,” says Cowgill. “It was the most fascinating non-sight I ever saw.”

On the desert and far from any railroad tracks, the prior probability that a train will pass by—and disappear into the earth—is virtually nil. Seeing it was not reason enough for Cowgill to believe it and should not have been. In short, the more preposterous the belief—that is, the lower its prior probability—the stronger the evidence needed to support it. As Sherlock Holmes says in The Valley of Fear:

I ought to know by this time that when a fact appears opposed to a long train of deductions, it invariably proves to be capable of bearing some other interpretation.

And this applies even if what is opposed to the long train of deductions is a long train of Southern Pacific rail cars.

9.4.2 What Authorities Have Reported

Reports from authorities make up one important part of your experience. (They are part of your experience because the reports are themselves something that you see or hear.) An authority is simply someone who is presumed to be in a better position than you to know the truth about the premise in question. This superiority may be due to either special ability or special access. A scientist or expert may have special ability to evaluate certain information; an eyewitness or a journalist may have special access to certain information.

As noted in Chapter 8, appealing to authority should be scrupulously avoided in circumstances where you are just as capable as anyone else of thinking through a view. In such cases, appealing to authority merely promotes intellectual timidity and can undermine the virtue of intellectual honesty. But we are quite right to rely on the authoritative reports of others for vast numbers of our beliefs, including most of our beliefs about science, history, and current affairs. There are two questions that you should ask to be sure that your use of authority is appropriate.

The first question is, How reliable is the authority’s report, given the circumstances?

A variety of circumstances can undermine the reliability of an authority’s report. A witness’s memory can be subject to “creative” forces of which the witness is unaware. Or an expert might be an expert—but on a different topic. But perhaps the most important undermining circumstance is conflict of interest. It would ordinarily be in the best interest of most authorities to be reliable. But that interest can be overridden by other competing interests. This can be a problem for journalists, for example. One media critic, David Shaw of the Los Angeles Times, identifies what he calls several “basic flaws in the way the contemporary news organizations function.” They include the following: “Pack journalism. Laziness. Superficiality. Cozy relationships with prosecutors. A competitive zeal that sends reporters off in a frantic search to be first with the latest shocking allegation, responsible journalism be damned. A tradition that often discourages reporters from raising key questions. . . .”

Like journalists, trained experts can also be rendered less than reliable due to overriding interests. Note, for example, this brief item from the Chronicle of Higher Education:

The spring sale catalog from LSU Press includes ads for a collection of essays by Cleanth Brooks and one by Louis Rubin. The blurb for the Brooks collection calls him “our best critic” and continues, “These essays are vintage Brooks.” The blurb for Rubin’s book calls him “one of the very best of our literary critics” and goes on to affirm that “these essays are vintage Rubin.” Curiously, the commendation for Brooks comes from the pen of Rubin, whose commendation comes from—you guessed it—Brooks.

This provides no reason to think that either Brooks or Rubin is deceiving us; but they do apparently have a conflict of interest, and thus we should have more to go on than their reports if we are to confidently believe that either of them is “among our best critics.”

The second question is, How probable would the statement be if you had no report from the authority? As in the last section, a more technical way of putting this is to ask what the prior probability of the statement is, where prior simply means supposing you had no report from the authority. If a normally reliable witness reports seeing green men come out of a spaceship or Elvis come out of a deli on Broadway, that should not be enough to persuade us. If a normally reliable scientist reports success in building a perpetual motion machine or in achieving cold fusion in a tabletop apparatus, we should reserve judgment until additional evidence is amassed. Improbable things often do turn out to be true. But the more improbable it is, the less ready we should be to accept it solely on the report of an authority.

Sometimes a report will reach you after passing through a chain of authorities. Your friend may tell you that she heard on the news that a scientist has made a certain new discovery. Every link in the chain—your friend, the newscaster, and the scientist—must be reliable; and the more improbable the discovery, the more reliable each must be. And note that there are probably other links that you do now know about—the individuals or services, for example, who got the information from the scientist and passed it on to the newscaster. Those links must also be reliable.

9.5 Strategies for Evaluating Premises

To evaluate the truth of a premise is to consider its epistemic probability—that is, to consider the quality of your evidence for it. How should you describe this evidence in the relevant portion of your evaluation of the argument?

9.5.1 The Reasonable Objector over Your Shoulder

In evaluating premises, try not to focus on what others—say, your peers or professors—expect you to believe or what beliefs they might find impressive. A much better place to start is by asking yourself what you actually do believe, more or less instinctively, about the premise, and what your actual evidence seems to be for that belief. And be sure that what you settle on is a real reason and not merely a restatement of the premise in slightly different words (nor a restatement of the denial of the premise, if you take it to be false).

As you think about the premise, remember the strategy of writing your evaluation as though there is a reasonable objector looking over your shoulder. Thus, you must satisfy someone who has roughly the same evidence that you have and who possesses the intellectual virtues of honesty, critical reflection, and inquiry. This may help you to keep the intellectual virtues in the forefront of your mind, in ways such as this:

• Exhibit critical reflection by asking what your evidence is, whether it supports your belief, and whether either your evidence or your belief can be improved.
• Exhibit inquisitiveness by seeking more evidence if it is meager (and withhold judgment if there is no opportunity to seek further evidence).
• Exhibit intellectual honesty by insuring that your chief objective in evaluating this premise is to know whether it is true or false regardless of your prejudices. Try to identify your own biases and habitual modes of thinking, and watch for them as you evaluate your evidence.

In your evaluation of every premise, you will provide your judgment and your defense of that judgment. Given that you will be doing this with a reasonable objector over your shoulder, you should also be prepared to provide, where necessary, a brief response to reasonable objections that might be raised. To the premise All swans are white, for example, we’ve already seen the following sample evaluation:

Premise 1 is almost certainly false, since I personally saw a black swan at the local zoo.

But black swans are rare; since the prior probability of your sighting is quite low, a reasonable objector is likely to object that it is best to remain unpersuaded until stronger evidence comes along. Your evaluation is much stronger if you anticipate that objection and deal with it in advance; here is one way you might do that:

Premise 1 is almost certainly false, since I personally saw a black swan at the local zoo. I realize, of course, that they are quite rare; so I made a special effort to be sure that I got a good look and wasn’t being misled in any way. I checked with others around me and they agreed that they also saw a black swan.

At this point, the objector would probably have to be unreasonable to continue to object.

Or consider the premise If air sacs in birds play a role in their breathing, then carbon monoxide introduced into the air sacs will kill them. Our sample evaluation goes something like this:

Premise 1 is probably true, since carbon monoxide interferes with the ability of blood to carry life-sustaining oxygen.

How might a reasonable objector find fault with this? One sensible objection might be that nothing has been said here about how much carbon monoxide it takes to have this effect, nor how much is being administered to the birds. It might be better to say can’t decide, due to the limited information. You have two choices at this point: concede that the objector has a good point (as always, since by definition the objector is reasonable!) and revise your judgment to can’t decide, or revise your defense slightly, as follows:

Premise 1 is probably true, since carbon monoxide interferes with the ability of blood to carry life-sustaining oxygen. This, of course, is based on the assumption that the scientist who is conducting the experiment is competent enough to know how much carbon monoxide is required and to introduce at least that much into the air sacs.

This seems to be a reasonable assumption and should satisfy the objector.

Let’s look at one more example, the premise Not many people are qualified to work as lifeguards. The sample evaluation is this:

Premise 1 is almost certainly true, since lifeguards must be in excellent physical shape, must be able to swim well, and must have extensive training—qualifications that are rare.

I can’t think of a reasonable objection to this defense and thus would leave the evaluation as it is.

These guidelines apply to any judgment you have about the premise—even if it is can’t decide. When you cannot decide, explain why you cannot decide. Chances are it will be because the evidence—whether there is a lot or a little—is balanced. In these cases, state the best reason you can come up with on each side. Don’t feel that you must force a decision, but don’t use cannot decide as an excuse for not thinking. When you do use it, be sure to show that you have thought carefully about it.

9.5.2 Thinking Backward and Thinking Ahead

As you consider your evidence, one natural strategy is to think backward—to look for what seems to have led you to believe or disbelieve the premise. Almost all of the examples provided so far have been of this sort. Why do I believe that all triangles have 180 degrees? I think back and recall that I learned it as a definition in high school geometry. Why do I not believe that all swans are white? Because I think back to my sighting of a black swan at the zoo. Other examples are easy to come by. Suppose you clarify an argument that has the following premise:

1. For any liquid, its freezing and melting temperature is the same.

Plausible though this may be, you realize that it is probably false on thinking back and recalling a magazine article you once read. You might then evaluate it in this preliminary way:

Premise 1 is probably false. Science News, which is normally a very reliable publication on matters of science, recently carried a story about the discovery of fish that live in very cold waters; their blood has a very low freezing temperature, even though, once frozen, the melting temperature is far higher.

In this way, by thinking backward you are able to appeal to a reliable authority.

But another useful strategy is to think ahead. This second strategy can take one of two forms. One way of doing this is to assume that the premise is true and see if anything obviously false follows from it; if so, that would show the premise to be false. Suppose, for example, the premise is this:

1. The meaning of any word is the thing that it picks out in the world.

This might seem superficially plausible. But you might arrive at the following evaluation:

Premise 1 is very probably false. It entails, for example, that the word unicorn has no meaning; for there are no unicorns, and thus the word picks out nothing in the world. But this is absurd—it is self-evidently false. The word unicorn is obviously meaningful, otherwise we wouldn’t know how to check and see whether there were any unicorns.

In this example, by thinking ahead you have run into a consequence that is self-evidently false; for by understanding the very meaning of the term, you understand that the word unicorn is meaningful.

Another way of doing this is to assume that the premise is false and see if anything obviously false follows from that; if so, then that would show the premise to be true. Suppose, for example, there is a premise such as this:

4. It is sometimes morally acceptable to break the law.

Your preliminary evaluation might be as follows:

Premise 4 is very probably true. Assume it is false. This would mean that it is never morally acceptable to break the law. But this would mean that you would be morally obligated to obey the speed limit even if driving faster would save someone’s life. But this is absurd. Since this absurdity results from assuming that the premise is false, the premise is very likely not false.

These two forward-thinking strategies search for implications that are absurd, concluding that the assumption that led to the absurdity must be rejected. Because they attack the assumption indirectly, via its implications, they are known as indirect arguments. They are also known as reductio ad absurdum arguments, since they aim to reduce the assumption to absurdity.

Such arguments can be effective but should be used with care. It is always possible that the absurd implication is produced not by the falsity of your assumption about the premise, but by some other false assumption that you are implicitly making. In the first case, for example, someone might argue that the mistake doesn’t lie in the premise The meaning of any word is the thing that it picks out in the world, but in this additional assumption: The word “unicorn” picks out nothing. Perhaps there really are unicorns (and thus the word picks out unicorns). Or, safely assuming that there are no unicorns, perhaps it picks out the idea of unicorns; in that case it does pick out something, so it is meaningful. This sort of mistake—failing to blame a false secondary or implicit premise—is common enough that it long ago earned a name of its own: the fallacy of non causa pro causa (i.e., the absurdity is not caused by the cause that is set forth).

Note that the practice of assuming there is a reasonable objector over your shoulder applies to indirect arguments as well. And you should be prepared for the possibility that your reasonable objector will accuse you of committing the fallacy of non causa pro causa. Return to the premise The meaning of any word is the thing that it picks out in the world. The evaluation, as it now stands, is as follows:

Premise 1 is very probably false. It entails, for example, that the word unicorn has no meaning because there are no unicorns, and thus the word picks out nothing in the world. But this is absurd—in fact, it is self-evidently false. The word unicorn is obviously meaningful, otherwise we wouldn’t know how to check and see whether there were any unicorns.

But it is stronger if you append the following sentences to it:

It might reasonably be objected, however, that the word unicorn does pick out something—namely the idea of unicorns (and thus, the fault would lie in the assumption that it does not pick out anything; the fault would not lie in Premise 1). But this objection cannot be right, because the objector would then have to admit that there are indeed unicorns in the world—since the objector says that unicorn means idea of unicorn, and the idea indeed exists even though unicorns do not.

Again, in this way you identify what is probably the weakest part of your defense and convince yourself (by convincing the reasonable objector over your shoulder) that your indirect argument is successful after all.

9.5.3 Fallacies and Truth

Sometimes false beliefs are branded as fallacies. In Aristotle to Zoos, for example, P. B. and J. S. Medawar write,

It is a popular fallacy that chewing gum regains its flavor if removed from the mouth and parked, say, under a chair. What is regained is not the flavor but the ability to taste the flavor as sensory adaptation wears off.

This is not a misuse of the term; a fallacy, recall, is an easy-to-make intellectual mistake, and there are many mistakes about truth (such as believing that chewing gum regains its flavor overnight) that are easy to make.

But although this is not a misuse of the term, it is not helpful in evaluating the premise. To say the premise Chewing gum regains its flavor overnight commits the fallacy of believing that chewing gum regains its flavor overnight is simply to say that the premise is false (note that the terms fallacy and false are closely related) and that a lot of people think it is true. It does not tell us anything about why people make the mistake, which is what it must do if it is to be useful in an evaluation. The other uses of the term fallacy that we look at in this text are generic. They tell us something about why an argument has gone wrong, regardless of the subject matter of the argument. The fallacy of equivocation, for example, can occur in any argument where the meaning of a word might shift—which is to say, in any argument. It can occur in an argument about gum (which might shift from chewing gum to the flesh under the teeth); and—to simply reverse the word—it can occur in an argument about a mug (which might shift from a cup to a face—reaffirming the many slips ‘twixt cup and lip). When we identify such a fallacy we are saying that the argument has gone wrong, in part, because of such a shift.

Since the point of your evaluation of each premise is to defend your judgment in a way that would satisfy the reasonable objector over your shoulder, it is best to skip the unhelpful step of accusing a premise of committing a fallacy. Instead, go straight to the explanation of why you believe it to be false. No need to bother saying, for example, that the belief commits the fallacy of believing that chewing gum regains its flavor overnight. Better simply to say that the premise is almost certainly false, and that the reasonable objection that our experiences support the premise—since the gum always does taste better the next morning—is explained by a change that occurs in our sense of taste (due to sensory adaptation) and not by any change in the gum.^[7]

9.6 Summary of Chapter Nine

Although people often reasonably disagree about the truth of a premise, that does not mean that what is true for one person may be false for another. Truth has to do with whether a belief fits with the world. It is not relative to the believer. This is consistent with the law of noncontradiction, which says that a statement cannot be both true and false, and with the closely related law of the excluded middle, which says that it must be either true or false. These two laws are valuable practical guidelines in thinking about truth.

Evidence, however, is relative to the believer; so evaluations of premises must be made in shades of gray. The best you can hope for is to evaluate a premise’s epistemic probability—that is, how strong your evidence is for its truth or falsity—using expressions such as probably true and probably false. One alternative notion of probability, subjective probability, is simply a measure of how much confidence you have in the truth of a belief; you should attempt to match your subjective with your epistemic probability.

Some of your evidence will be found in other beliefs of yours—that is, it will be inferential. But some of it—self-evidence and experiential evidence —will be noninferential. Self-evidence is what you have when the premise itself, by virtue of the very meanings of the words, provides you with all the evidence you need to make a reasonable judgment. Experiential evidence is what is provided by the observations that you make with any of your five senses. One important category of experiential evidence is reports that you hear or read from authorities who have special access to information or special abilities to evaluate it.

For any experiential evidence, it is important to be aware of circumstances that might undermine its reliability. It is also important that you require more evidence whenever the prior probability of your belief is extremely low.

In preparing your evaluation, ask yourself what you really think, both about the premise and about your evidence for or against it. You might do this by thinking backward about how you arrived at your belief or by thinking ahead to see whether you can produce an indirect argument. As you do so, keep in mind the intellectual virtues of honesty, critical reflection, and empirical inquiry. Then present your evaluation for each premise by stating your belief, your evidence for that belief, and, if there is a reasonable objection, a brief response to it as though there is a reasonable objector over your shoulder.

9.7 Guidelines for Chapter Nine

• For practical purposes, assume that no statement is both true and false and that every statement is either true or false.
• If it looks as though the truth-value of a statement will be different depending on who expresses it, it is usually because the statement is referentially ambiguous. Look for the ambiguous term, which may be implicit, and eliminate the ambiguity before evaluating its truth.
• The rare statements that appear to violate the two laws of truth, yet do not merely suffer from a referential ambiguity, should be evaluated as can’t decide, with an explanation.
• Evaluate premises according to their epistemic probability—that is, according to how strong your evidence is for their truth or falsity—using expressions such as probably true and probably false.
• Aim to match your subjective and epistemic probabilities—that is, to have the amount of confidence that is warranted by the evidence.
• If a premise can charitably be seen to be almost certainly true or false solely on the basis of your understanding of the meanings of the words within it, evaluate it as self-evidently true or false.
• Stipulative definitions, in which the arguer offers a revised or new definition for a term, may be considered self-evidently true. But be sure that arguments with such definitions do not commit the fallacy of equivocation.
• Observations made by any of your five senses can provide powerful evidence in evaluating your beliefs. Be on the alert, however, for circumstances that can weaken them.
• Reports of authorities can provide powerful evidence in evaluating beliefs. Be on the alert, however, for circumstances that can weaken them.
• For each premise, state your judgment, your defense of the judgment, and, where relevant, a brief response to any objections that might be posed by a “reasonable objector over your shoulder.”
• Ask yourself what you really think about the premise and your evidence for or against it. You might do this by thinking backward about how you arrived at your belief or by thinking ahead to see whether you can produce an indirect argument (though you should avoid the fallacy of non causa pro causa in doing so). As you do so, keep in mind the reasonable objector over your shoulder.
• Instead of accusing any premise of committing a fallacy, focus on explaining why you believe the premise to be false.

9.8 Glossary for Chapter Nine

Authority—someone who is presumed to be in a better position than you to know the truth about a statement. This superiority may be due to either special ability (as with a scientist or expert) or special access (as with an eyewitness or a journalist).

Epistemic—having to do with knowledge.

Epistemic probability—the likelihood that a statement is true, given the total evidence available to you—that is, given all of your background beliefs and experiences. This is the notion of probability that should be used in your evaluation of premises. To say that a premise is probably true is, then, just to say that you have fairly good evidence for its truth.

Experiential evidence—evidence provided by sense experience—that is, that which is seen, heard, touched, smelled, or tasted. It is one kind of noninferential evidence.

Fallacy of non causa pro causa—the mistake in an indirect argument of relying on a secondary assumption—often implicit—that is false, so that it is really the secondary assumption that should be blamed, not the assumption blamed by the arguer. (It literally means that the absurdity is not caused by the cause that is set forth.)

Frequency probability—the likelihood that a specific thing has a property, based strictly on the frequency with which all things of that sort have the property.

Indirect argument—an argument that shows a statement is false by showing that it leads to an absurd consequence. This is sometimes, alternatively, used to show that the negation of the statement is true (which amounts to the same thing as showing that the belief itself is false). Sometimes also called a reductio ad absurdum argument or, for short, reductio.

Inferential evidence—beliefs that are appealed to in support of another belief (which is inferred from them).

Law of the excluded middle—every statement is either true or false. It follows from this that there is no middle ground between the true and the false.

Law of noncontradiction—no statement is both true and false. It follows from this that truth is objective and absolute—there cannot be any statement, for example, that is true for you but false for me.

Noninferential evidence—things other than beliefs that are appealed to in support of a belief. This includes self-evidence and experiential evidence.

Prior probability—the epistemic probability of a belief independent of (i.e., prior to) a specified piece of evidence. When considering, for example, the prior probability of something you heard, its prior probability is simply how probable it would be if you had not heard it.

Self-evidence—evidence that comes from understanding the very meanings of the words themselves in a statement. Statements that are self-evidently true or false can be seen to be true or false largely by virtue of understanding the words of the statement. Philosophers sometimes refer to these statements as analytic a priori statements; they are also sometimes described as statements that are seen to be true or false by definition.

Stipulative definition—a nonstandard definition for a term, decreed by a speaker or writer for some specific use.

Subjective probability—the degree of confidence you have that a given statement is true. It is entirely relative to the believer; there is no fact of the matter over and above the believer’s level of confidence.

Truth-values—evaluations, like true and false, which can be given of how well a statement fits with the world.