Published online by Cambridge University Press: 12 March 2014
A. N. Prior in [9] has suggested an approach towards a second order logic of existence where, following medieval logicians, we distinguish “between predicates (like ‘is red’, ‘is hard’, etc.) which entail existence, and predicates (like ‘is thought to be red’, ‘is thought of’, etc.) which do not.”2 Let us refer to attributes (including relational attributes) which are designated by the former kind of predicate as existence attributes, or for brevity, e-attributes.
I am indebted to the referee for helpful suggestions in revisions of an earlier draft of this paper. For a more philosophical discussion of the present system, especially of the substitution free form of its axiom set, cf. [7].