Descriptive vs Prescriptive

by Mortimer J. Adler, Ph.D.

A prescriptive statement or judgment is one that asserts what ought or ought not to be done. A statement about what ought or ought not to be desired imposes a prescription that may or may not be obeyed. In contradistinction, a descriptive statement or judgment is one that asserts the way things are, not how they ought to be. A statement about what is desired by a given individual simply describes his condition as a matter of fact.

How, it is asked, can prescriptive injunctions be true or false? Have we not adopted the view that the truth of statements or judgments consists in their conformity with the ways things areÑwith the facts that they try to describe? If a statement is true when it asserts that that which is, is, and false when it asserts that which is, is not, how then can there be truth or falsity in a statement that asserts what ought or ought not to be?

Even if we possessed all the descriptive truth that is attain able, how could our knowledge of reality, our knowledge of the way things are, lead us to any valid conclusion about what ought to be done or about what ought to be desired?

It was long ago quite correctly pointed out by the skeptical philosopher David Hume that no prescriptive conclusion (in the form of an “ought” statement) can be validly inferred from a set of premises, no matter how complete, that consists solely of descriptive statements about the way things are. Even if we had perfect knowledge of all the properties that enter into the description of an object, we could not infer the goodness of the object or that it ought to be desired.

We are thus confronted with two obstacles, not one. The first is the difficulty raised by the question, How can prescriptive statements be either true or false, if truth consists in the correspondence between what is asserted and the way things are? The second is the objection raised by David Hume, to the effect that truths about matters of fact do not enable us to reach by reasoning a single valid prescriptive conclusionÑa true judgment about what ought or ought not to be done or desired.

Unless we can surmount these difficulties, no prescriptive statement or judgment can be true or false. If we cannot truly say what ought to be desired, then the good is the desirable only in the sense that it appears good to the individual who in fact desires it. Acquiescing in the rejection of the alternative sense of the desirable as that which ought to be desired, we also must give up the notion that some objects are really good as distinguished from other objects that only appear to be good and may not be really so.

To refute the skeptical view, which makes all value judgments subjective and relative to individual desires, we must be able to show how prescriptive statements can be objectively true. An understanding of truth as including more than the kind of truth that can be found in descriptive statements thus becomes the turning point in our attempt to establish a certain measure of objectivity in our judgments about what is good and bad.

Only through such understanding will we be able to show that some value judgments belong to the sphere of truth, instead of all being relegated to the sphere of taste and thus reduced to matters about which reasonable men should not argue with one another or expect to reach agreement.

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