A Hybrid Predicate Calculus∗

We present the Hybrid Predicate Calculus (HPC), a hybrid logical system which incorporates a fairly conventional first-order predicate calculus, but which also include elements of modal logic and relational algebra. A special effort has been made to produce a (syntactically and semantically) well-integrated whole, rather than just a disjoint union. Our calculus, from a formal point of view, is equivalent (in terms of expressiveness) to conventional first-order systems. It exhibits, however, some promising pragmatic advantages. In particular, many statements of so-called “everyday” language can be formulated more directly and concisely, often without resort to any bound variables.