This chapter presents some considerations concerning combinatory logic which this chapter by Quine has suggested. It turns to the question of the ontology of combinatory logic, because it is necessary to be clear about it in view of the constant reference to ontological questions in the work of Quine and philosophers of similar persuasion. In the situation of Quine the operators operate on one or more "predicates" to form another predicate, not necessarily with the same number of arguments. The system proposed by Quine is such that the "operators"—which are partly combinators, and partly combinations of combinators and other logical notions—are applied directly to predicates. There are two kinds of such operations. The first kind are simply combinators; the second kind are combinations of combinators with operations from ordinary logic, viz., negation, conjunction and existential quantification. Combinatory logic can be applied to ontological situations of various sorts, and, except in a very broad sense.