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The Nature of Truth

Is truth absolute? Is truth just opinion?
Truth as a predictive model

It should be made clear from the onset that the sort of truth we are talking about in this discussion is not some sort of idealized dogmatic or universal truth of the type sometimes promoted by religious or political zealots. While truth is an extremely valuable concept, things are usually not totally true or totally false, and we may or may not be able to judge the truth of a statement with much confidence. Still, some things are very true and others are very false, and it is often important that we can make good judgments about which is which and when we don't know.

Sometimes problems come up as to whether truth is real or well-defined. Part of the problem is that the contexts where we talk about truth can vary dramatically. Consider the following statements:

  • Julius Caesar was the first emperor of Rome. (historical statement)
  • The football game starts at 1:00. (statement of specific detail)
  • Energy can be neither created nor destroyed. (statement of great generality)
  • Pavarotti is a better singer than Elton John. (statement involving taste)
  • We are all one with the universe. (untestable statement)
  • You shouldn't steal things that belong to other people. (moral/ethical statement)
  • Two plus two equals four. (mathematical statement)

The first three statements (historical, detail, generality) involve the most common sort of truth. I think it is good to look at them as models. They construct a description of some aspect of reality. The words represent parts of reality and it is implied that the relationship between the corresponding real things is the same as the relationship implied by the statement. For the truth of a statement to be meaningful, it should be predictive in some way. If we say the football games starts at 1:00, that implies that witnesses in the appropriate place will observe a football game going on shortly after 1:00 but not before 1:00. If a statement doesn't predict anything, it is hard to imagine how the statement could be of any use to us.

It may seem odd that a historical statement would be predictive, but this is still reasonable since it does predict that evidence we observe will be consistent with this statement. It predicts that copies of ancient writings and engravings on unearthed tablets and any other consequences of the identity of the first emperor of Rome will be consistent with the model that this person was Julius Caesar.

The principle of physics that energy cannot be created or destroyed is more typical of what we consider a predictive model, and scientists design experiments to see if such predictions are confirmed.

The issue of whether we are all "one with the universe" does not make any prediction as far as I can see. It is hard to see how evidence could be evaluated for or against such a statement. In such a situation the truth of the statement is effectively meaningless, so there is no point in debating whether it is true or false.

The question of whether Pavarotti is better than Elton John presents a special problem because there is no agreed upon definition of what makes a singer better. We might agree about who can sing a higher note or hold a note longer, but if one person prefers Pavarotti and another prefers Elton John, there is no way we can show that one is right and the other is wrong. Unfortunately there is a tradition that experts in an area like music sometimes regard their own preferences as a "truth" that one thing is better than another, and those of us who are not experts may believe them because we feel unqualified to question their opinions. In modern times some might challenge such arbitrary choices by saying "It is true for you that Pavarotti is better but it is true for me that Elton John is better." This leads to the idea that there are different "truths" for different people. This might be fine for evaluating artists, but it gets us into big trouble when talk about the conservation of energy or when the football game starts or whether there is a cement truck heading toward our car at high speed. The problem of truth involving preferences is better resolved by saying that it is true that you prefer Pavarotti and that I prefer Elton John (this is a hypothetical example by the way).

The problem of moral and ethical statements is similar in that there is no agreed upon rule for how to determine whether they are true. The method above for truths involving preferences could be employed, but it isn't very satisfactory. If we say "Stealing is wrong for you but it's not wrong for me," people aren't going to be very happy. Many individual questions might be resolved if the people debating the question agree on the ultimate purpose they want to achieve. For example, virtually all moral and ethical systems agree that we should try to avoid killing people, so a debate about which of two possible military actions is most ethical might be resolved by gathering and analyzing evidence as to which would cause the fewest deaths.

Unfortunately, many of the most serious disputes such as abortion, sexual morality, and demands for particular forms of religious worship cannot be addressed this way because they involve fundamental differences in the definition of morality. By considering the basic nature of morality it might be possible to make some progress on such issues; otherwise we might hope a rational examination of how each of us arrived at our moral beliefs would help people realize that their own basis is not guaranteed to be more valid than someone else's. This would hopefully reduce the chances of bitter confrontations with people who make different moral assumptions.

The case of the mathematical statement is special because, unlike scientific statements, the truth of such statements follows totally from the definition of terms and axioms, and not on any observation of the real world. Generally truths involving the real world involve measurements that have some degree of inaccuracy and generalizations for which exceptions may be found in the future. In mathematics (which includes formal logic) it is reasonable to consider some statements to be perfectly true and those which are not perfectly true to be utterly false. We should be careful to recognize that real world statements tend to become useless if they are held to such an extreme standard, since few things are totally true or totally false.

Definition vs. substance

If there is a question about the truth of a statement, it might be because there is a misunderstanding about the meaning of the words, or it might be because there is a disagreement about the predictions implied by the statement and what evidence would tend to confirm or deny it. If, for example, you claimed that Fred was a heavy drinker, and I claimed that he wasn't, it might seem that we have differing opinions about how much drinking Fred does.  On the other hand, we might agree on how much he drinks, but we disagree on what is meant by a "heavy drinker".  

It is important to recognize when a dispute is about definition rather than substance in order to avoid a great deal of irrelevant debate.

Philosophical attacks on the idea of truth

Some philosophers, particularly those identifying themselves as "postmodernists", assert that truth is not absolute, but depends upon the individual point of view. They regard truth as political - what's true depends on your political ideology. Science is regarded as just another belief system. I don't see this as a viable point of view. If I tell a blind man that it's safe to cross the street, and he gets hit by a truck, it isn't valid for me to say "it was true for me that it was safe for him to cross the street." He was depending on a kind of truth that is more than just a point of view.

Postmodernists' views seem more reasonable when applied to things like art and morality, where there are no widely agreed on ways to determine what is true. Even in these areas, we can benefit by gaining a better understanding so issues of truth are better defined. In traditional scientific areas, postmodernists correctly point out that there is always an element of opinion and bias in scientific work. While this is so, scientific methods are carefully designed to keep such biases to an absolute minimum, which would not normally be the case when using emotional or political or religious methods to reach conclusions.

Vagueness & information content

True statements contain information. It can be useful to consider the amount of information contained in a statement, and this subject is considered in detail in the study of information theory. In general, vague statements, like blurry pictures, contain less information than precise statements. Unreliable statements (those with a significant probability of being false) can be considered to contain less information than reliable ones. Other factors affect the value of information, such as how useful it is and whether it is already known to the recipient.


We can consider all knowledge as having a probability associated with it. Do I know that the floor of my house will support my weight, because it has in the past? I feel that is extremely probable, but there is some tiny possibility that something has recently undermined it. I am very confident that the world is roughly spherical. I am pretty sure that eating fatty foods increases my risk of heart attack. We often think of probability as only applying to the future, but as long as we have some doubt about the answer to a question, the concept of probability can apply to the past and present as well. If we deal one card from a deck of playing cards to a friend, the probability of it being an ace would be 4 in 52. As far as we are concerned, the fact that the card has already been determined does not affect our judgment of the probabilities. If we then also deal a card to ourselves and see it is an ace, the chances of our friend having an ace is now 3 in 51 (three out of the 51 cards we cannot see are aces), while if we don't have an ace the probability would be 4 in 51. When we learn more about a situation, the probabilities of certain facts change accordingly.