 The rule is that for every thought, there is an object of thought. Prior and many other have objected to this: Prior’s counterexample is “I am thinking of nothing” (Prior 1971: 122–123). But these counterexamples only work if the sentences that express them are true. One wonders if one can think of nothing, or whether what is referred to in “thinking of nothing”, is, as older people often experience, an unnoticed bout of unconsciousness.