ABSTRACT
A chain of argum ents, leading from a set M of assum ptions to a claim v , is called a deduction o f v from M . I shall not specify here which of the many conceivable kinds of arguments may have been used in such a deduction; I only assume the reader to know that there are linguistic objects which in daily conversation are considered deductions. But among those many kinds of arguments a few can be isolated as being connected w ith the usage of the logical phrases them selves - e .g . w ith and and or. In order to talk about them without am biguity, I shall consider claims and hypotheses to be propositional form ulas; I shall abbreviate the presence of a deductive situation, leading from M to v , by expressions such as M = > v .
