This paper presents different types of clausal constituents of the main (matrix) clause in Hausa which are formally independent. Their status of independent (or sentence-initial) clauses is determined by the use of finite verbs in their non-relative form. These clauses are put in place where the nominal constituent is expected in a clausal context. The language sources provide us with the examples of a finite clause following the preposition, genitive linker and pre-object form of the verb. Other manifestations of these structures are simultaneous clauses which are interrelated, as well as fixed clausal phrases with nominal agreement. It is shown that what is marginal or exceptional in some other languages, in Hausa is a part of the regular grammatical means of expression. Along with well-established patterns, 'clauses within clauses' may be also variants of the nominalized structures, which have certain stylistic connotation. This differentiation of clausal constituents within the matrix clause in Hausa is viewed as manifestation of different stages of their grammaticalization which refers to the placement of the clausal structure within a nominal slot.