THE DECLARATIVE CLAUSE TYPE
The declarative is the basic clause type, with Subject-Finite ordering, as in:

The Finite, specified for tense or modality, is always the first or only element of a verbal group. It is realized by either a verbal operator (was, will, has, etc.), as in 1 and 2, or a tensed (past or present) form of the lexical verb, as in 4 and 5. The primary verbs function both as operators 1 and as main verbs 3:

More exactly, in positive declarative clauses, Finite and Predicator fuse in the present and past tensed forms of lexical verbs and of be and have when used as main verbs. The operator is always realized by a verb: primary, modal or do.
The Finite element relates the proposition to a point of reference: either a time reference, by tense, or the speaker’s judgement by means of modality.