When we ask for explanations of processes or events, we normally are seeking an understanding of what entities act to produce them and what attributes of those entities make such actions possible. In effect, when someone asks, "Why is X?"—what that person usually means is: "What makes X, rather than some alternative, metaphysically possible?" For example, if we ask why an apple falls to the earth, we seek an explanation of that action in terms of the nature of the apple, the earth, and any other entities that might be involved.

Since the logical law of identity requires that the earth, apples, and other entities conform to their own natures, explanations of this kind are logically compelling and sufficient. As an illustration of insufficient explanation, one might consider the popular mathematically based "econometric models" that purport to describe economic activity, while failing to relate such activity to the underlying nature of acting human beings.