As it was shown in§15 Syntax is to be defined in two ways: according to the units described in it and according to properties of the units.
The units which are explored with the syntactical methods is Sentence. You know it from school. And it is true, and even more than true, because, as we found if §2, grammatical studies have to embrace not only oppositional semantic features of units but all information about the units. The units liable to syntactical studies are sentences and their parts, structures made by connection of words, and functions of words in sentences and word combinations (phrases). But the results of grammatical analysis of Syntax includes not only the system syntactical categories based on opposition of forms of sentences, but also complete (if possible) description of all meaning that sentences can express. It means that description of Syntax has not two, but three divisions — alongside with paradigmatic and syntagmatic Syntax we find semantic Syntax, dealing with sentence meaning.