Studies of syntax in first language acquisition have so far concentrated on the propositional side of the sentence, i.e. on the occurrence and interplay of semantic roles like agent, benefactive, objective, etc. and their syntactic expression. The modality constituent, however, has received little attention in the study of child language. This may be due in part to the impetus more recent research in this field has received from studies of the acquisition of English, a language with poor verb morphology as compared to synthetic languages. The research to be presented in this paper is concerned with an early stage of the acquisition of Modern Greek as a first language, a language with a particularly rich verb morphology. Since modality, aspect, and tense are obligatorily marked on the main verb in Mod. Greek, this language offers an excellent opportunity for studying the development of these fundamental categories of verbal grammar at an earlier stage than in more analytic languages. [...] As this paper is concerned with the semantic categories of verbal grammar mentioned above as weIl as with their formal expression, only utterances containing a verb will be considered. For reasons of space we shall further limit ourselves to those utterances containing a main verb. Such utterances divide into two classes, modal and non-modal. [...] In spite of Calbert's claim (Calbert 1975) that there are no strictly non-modal expressions, affirmative and negative statements as well as questions not containing a modal verb will be considered as non-modal. As will be shown below, modal and non-modal expressions are formally differentiated at the stage of language acquisition studied.