The present paper is concerned with the sentence structure in modern North Slavic languages, namely Czech, Polish and Russian. Proceeding from the classical distinction between form and meaning, a system is outlined where the grammatical categories of verbal mood and tense are uniformly encoded in I°, while inflectional markers appearing on verb forms below IP merely reflect them. Thus, both 'synthetic' and 'analytic' structures can be given a uniform analysis. Also, the notoriously vague notion of finiteness receives a minimalist definition in terms of ϕ-features and argument structure. This, in turn, makes it possible to account for the differences obtaining between operators and auxiliaries which are proposed to be distinct manifestations of I°. As such, they provide the respective structure with a particular mood and tense semantics. However, apart from this 'functional' class of auxiliaries, there is yet another type to be considered which might be called 'lexical' as it is void of any grammatical meanings whatsoever. The relevant forms are heads of VPs in the c-command domain of I° which render the respective periphrastic structure finite. They either reflect the presence of some mood–tense operator or satisfy selectional requirements of some auxiliary in I°.
