THE QUESTION

Solipsism poses a familiar epistemological problem. Each of us has beliefs about a world that allegedly exists outside our own minds. The problem is to justify these nonsolipsistic convictions. One standard approach is to argue that the existence of things outside our own sensations may reasonably be inferred from regularities that obtain within our sensations. Certain experiences, which I will call tiger sounds and tiger visual images, exhibit a striking correlation. We can explain the existence of this correlation by postulating an entity that is a cause of both. If there were tigers, it would be no surprise that certain sights and certain sounds tend to co-occur. Our rejection of solipsism can thus be justified by appeal to an abductive argument; we advance an inference to the best explanation conforming to the pattern that Reichenbach (1956) called the principle of the common cause (Salmon 1984; Sober 1988).

The epistemological problem posed by solipsism is an old chestnut. A quite different problem – one less often noticed, let alone addressed – is the problem of explanation. Why do we have beliefs about the world outside our own minds? To reply that it is in our nature to “reify” may be true enough, but it merely postpones the question at hand.