 The idea that the non-schematic expressions in logical forms, i.e. the logical expressions, are widely applicable across different areas of discourse is also present from the beginning of logic, and recurs in all the great logicians. It appears indirectly in many passages from Aristotle, such as the following: “All the sciences are related through the common things (I call common those which they use in order to demonstrate from them, but not those that are demonstrated in them or those about which something is demonstrated); and logic is related to them all, as it is a science that attempts to demonstrate universally the common things” (Posterior Analytics, 77a26–9); “we don't need to take hold of the things of all refutations, but only of those that are characteristic of logic; for these are common to every technique and ability” (Sophistical Refutations, 170a34–5). (In these texts “logic” is an appropriate translation of dialektike; see Kneale and Kneale 1962, I, §3, who inform us that logike is used for the first time with its current meaning in Alexander of Aphrodisias.) Frege says that “the firmest proof is obviously the purely logical, which, prescinding from the particularity of things, is based solely on the laws on which all knowledge rests” (1879, p. 48; see also 1885, where the universal applicability of the arithmetical concepts is taken as a sign of their logicality). The same idea is conspicuous as well in Tarski (1941, ch. II, §6).