1. Quine 1934a, 30.
2. This method was already used, but less explicitly, in NF, see Quine 1937, 82–83; 111.
3. In the preface to the 1981 edition, Quine writes: “Schemata could indeed have been admitted still as heuristic aids, and they would have made manipulations easier and more vivid; but I eschewed them for pedagogical reasons of a higher order. I feared that readers would persist in thinking of sentence letters and predicate letters as variables taking propositions and properties as values, protest as I might”, in Quine 1940, v; see also Quine 1966a, 273.
4. See Quine 1953c, 112: “These marks rightly suggest that the whole is, like an ordinary quotation, a substantive which refers to an expression…”
5. Quine 1940, 23.