When an explanation makes a fact intelligible, the mystery goes out of it. We understand it so well that we can hardly conceive of things being otherwise. Consider the simple mathematical fact that one plus one equals two. Once we understand elementary arithmetic, we no longer feel the urge to ask why one plus one equals two. That one plus one equals two strikes us as not merely true but unavoidable; we cannot even coherently imagine its falsity. Much of philosophy aims to bring other fundamental features of reality into a similar light, to make them appear not arbitrary but inevitable and, thus, intelligible.

This aspiration that philosophy render the world intelligible is best expressed by the German polymath Gottfried Wilhelm Leibniz and the Dutch philosopher Baruch Spinoza .…