 The purpose of formal logic, in Church’s view, was first and foremost to study the form of correct deductive reasoning in abstraction from its subject matter (1956a: §00). For Church, deductive reasoning operates on propositions, and so the study of such reasoning is the study of the logical form of propositions—which Church distinguished from their “content” or “matter” (ibid)—via the study of the logical forms of sentences that express them (ibid; cf. 1959 [BE: 475]). This way of studying logical form invoked what Church called the “logistic method” (1956a). This required him to distinguish between informal languages and formalized languages, because