  As we claim to have defined truth we ought to be able to substitute our definition for the word “true” wherever it occurs. But the difficulty we have mentioned renders this impossible in ordinary language which treats what should really be called pro-sentences as if they were pro-nouns. […] “that” and “what” even when functioning as short for sentences always require to be supplied with a verb: this verb is often “is true” and this peculiarity of language gives rise to artificial problems as to the nature of truth, which disappear at once when they are expressed in logical symbolism, in which we can render “what he believed is true” by “if p was what he believed, p” (1929c, [OT] 10, his emphasis).