ABSTRACT
Principles in the sense of non-derivative propositions are of two somewhat divergent types: (i) first premises, such as the axioms or postulates of a geometry which are actual constituents of the formal system, and (ii) basic assumptions and rules of operation, such as the principles of inference which govern the construction of the system though not actually included in the system itself. Principles of the first type may properly be described as constitutive because they actually belong to the formal system; principles of the second type are regulative because they afford rules to which the system
from the initial definition of p and p' as contradictories. Contradictories are by definition propositions whieh cannot be simultaneously true; the statement that p and p' can never be simultaneously true follows from the symbolic equivalence of ''p is true" and ''p' is false". The principle of contradiction may be stated in such a way as to exclude all factual reference and to emphasize its regulative function, namely, "Contradictory propositions should not be included in a single formal system"; in this form it makes no ontologie commitments whatsoever, but merely formulates and prescribes a rule for the construction of formal propositional systems.
