 For philosophers who accept the idea of formality, as we said above, the logical form of a sentence is a certain schema in which the expressions that are not schematic letters are widely applicable across different areas of  discourse.[6]  If the schema is the form of a logical truth, all of its replacement instances are logical truths. The idea that logic is especially concerned with (replacement instances of) schemata is of course evident beginning with Aristotle and the Stoics, in all of whom the word usually translated by “figure” is precisely schema. In Aristotle a figure is actually an even more abstract form of a group of what we would now call “schemata”, such as (2′). Our schemata are closer to what in the Aristotelian syllogistic are the moods; but there seems to be no word for “mood” in Aristotle (except possibly ptoseon in 42b30 or tropon in 43a10; see Smith 1989, pp. 148–9), and thus no general reflection on the notion of formal schemata. There is explicit reflection on the contrast between the formal schemata or moods and the matter (hyle) of syllogismoi in Alexander of Aphrodisias (53.28ff., quoted by Bocheński 1956, §24.06), and there has been ever since. The matter are the values of the schematic letters.