   The language of Mereology in 1916 used many expressions besides the specifically mereological primitive ‘part’: in addition to nominal variables, there are expressions forming sentences from nominal variables, as in ‘\(A\) is (a) \(b\)’, ‘\(A\) is \(B\)’, ‘every \(a\) is a \(b\)’, ‘some \(a\) is a \(b\), ‘no \(a\) is a \(b\)’, as well as words such as ‘object’ and ‘exist’. Complex names also occur in sentences, as the expressions ‘part of \(A\)’ and ‘ingredient of \(A\)’ in ‘every part of \(A\) is an ingredient of \(A\)’. Leśniewski had hitherto taken such logical bits of language for granted, but now he needed to formalize them. He wanted a logical calculus of names and the expressions involving them. There were precedents in traditional syllogistic, and more especially in the algebra of logic of Ernst Schröder, which Leśniewski looked at in coming up with his own system, based as in the case of Mereology on his intuitive understanding of the relevant expressions as carefully used in ordinary language. At first he gathered propositions he was sure were true, such as ‘If \(A\) is \(b\), then \(A\) is \(A\)’. We know about this one because it is mentioned, presumably scornfully, in a diary entry by Twardowski for 1 July 1919, as being the first axiom of the new system that Leśniewski was working on at the time. Leśniewski has left us a graphic description of his method of working at this crucial and fluid time of his development [Collected Works 366–9]: