  The fact that the basic sentence-module in Ontology is singular inclusion of the form ‘\(A \isa b\)’ has misled some commentators into thinking that Leśniewski turned his back on the Fregean notion of predication as functional application and instead reverted to a medieval “two-name” account of predication. Indeed, except for the matter of tense, Leśniewski’s account of the truth-conditions of such singular sentences—that they are true if and only if the subject term denotes a single object and the predicate term denotes one or more objects of which this is one—is almost exactly the same as that given by the medieval nominalist William of Ockham. However, whether or not Ockham was a two-name theorist, Leśniewski definitely was not. The general form of the singular sentence is the same as that of any binary predication, \(f(ab)\), or in Leśniewski’s notation, \(f\{ab\}\). Singular inclusion is no syncategorematic copula: it is a special binary predicate. That it is chosen as the primitive is understandable but not compulsory. Leśniewski knew that other predicates than ‘\(\isa\)’ could be taken as primitive, a fact emphasized later by Lejewski.