Empirical Equivalence, Real Semantic Difference

Even when two claims yield the same prediction, their truth content matters.

May 12, 2016Filed under theology#m. div.#philosophy#science#sebtsMarkdown source

The following was written in partial fulfillment of the requirements of Dr. Greg Welty's Philosophy: Science and Religion class at Southeastern Baptist Theological Seminary.


The following was prepared as a one-page, single-spaced short response to a question from the readings for this class.

When two theories make contradictory claims, even were they to have empirically equivalent outcomes, the contradiction in their claims is not merely terminological or semantic. It is fairly easy to conceive of claims are merely semantically different, but which have the same basic content: “That is a chair” and the Spanish equivalent “ésa es una silla” both have the same basic referents, and even intend broadly the same meaning. Their variance is terminological, by dint of being in two distinct languages. It is far more difficult to find two claims which are in opposition to each other, but their opposition is merely terminological.

This is not just the case in science. To make a claim, scientific or otherwise, is to assert something about the world as it actually is. Thus, “The sky is blue” and “The sky is green but appears to us as blue because all our eyes are defective in a way we cannot measure” would have the same base empirical content, but make very different claims about the nature of human sight and the sky. This particular claim is trivially testable in some other way; but different claims in fundamental physics—empirically equivalent string theories, for example—might not be trivially testable, or testable at all: they might be empirically equivalent in principle as well as in practice. But the trivial example serves to highlight the reality that empirical equivalence does not entail semantic equality. The blueness or greenness of the sky is not merely a matter of human descriptions of things. Rather, even though they are meaningful only because of their semantics, their semantics carry force that is not merely different ways of saying the same thing: that is one of the basic necessities for language to function. If different semantics did not actually entail different claims, communication would be impossible. Less pragmatically, if one affirms that the referents in question are in some sense “out there” and not merely the contents of human speech or human sense data—that is, if one embraces a correspondence theory of truth and a basically, albeit critically, realist view of human knowledge including scientific knowledge—then the notion that two claims are merely terminological variants even though their semantics stand in contrast is clearly false.

To take an example particularly appropriate to a science-and-religion course: it is quite conceivable that a disinterested god (quite different from the one we worship) and a pantheon of disinterested gods and a universe which came out purely by chance would all be empirically equivalent. Yet “there is one bored god out there” and “there is no god out there” and “there are many bored gods out there” are clearly and obviously not terminological variants of each other, even if there is no empirical way to tell them apart. A similar thing would hold of two string theories, one which postulated 12 and the other 28 hidden dimensions. Even if both yielded the same empirical predictions (which were verified) and were in-principle incapable of any further test, they would nonetheless be claims with semantic content about the nature of reality which is not reducible merely to a terminological variant. The fact that the truth or falsity of a claim may not be knowable does not tell against its distinctive semantic content, only against its pragmatic utility. If one of the two string theories suggested above were true, it might not make any practical difference which one it was. After all, if the contents are permanently inaccessible to humans, and the theoretical consequences identical, then either may be used in the pursuit of other knowledge. However, by dint of the fact that they make distinct and countervailing claims to one another, at least one must be false. And truth is no small matter!