  When he speaks of extending liberally the set of logical terms, Tarski is perhaps thinking of the phenomenon of what he calls the “disciplines preceding a given discipline” in Tarski (1937) (see p. 80). He speaks of logic as preceding every discipline, in the sense that logical constants and logical laws are presupposed by and form part of every science. But similarly, in developing a certain theory, not only logic but other theories may be taken for granted; thus Tarski speaks of logic and arithmetic as a conveniently presupposed basis of theories for the development of geometry. This would account naturally for the fact that Tarski was skeptical about the possibility of finding a sharp distinction between logical and extra-logical terms, for it might very well depend on the context of investigation what terms and what laws are considered as forming part of the “logic” of the investigation. 