ABSTRACT
In this chapter the authors are concerned with formulae as propositional formulae, with variables as propositional variables, with operators as proposition-forming operators; and similarly the rules are regarded as rules for generating propositional formulae. Formalization lays bare the structure, and, in particular, exposes areas of structural complexity and simplicity. At this point, it is convenient to set out in full the basis (i.e. primitives, rules, etc.) of a rather simple formal system. This will serve to illustrate some points already made, as well as some to be made subsequently. In particular, consideration of this example should make clear: the general structure of a formal system, the nature of interpretation and formalization and the relation between a formal system and an axiomatic system.
