Dependent clauses with vacant subject are considered in contraposition to independent clauses with vacant subject, which refer to interrogative sentences with unknown subject being sought by means of compulsory interrogative element. The languages particularly involved are English, Dutch and Swedish. Within the binomiality idea a formal modeling is undertaken to explain the syntactic nature of the formal particle in a subject. Main and secondary substantive / verbal sentence parts are assumed to consist of two parts — a space / time specifier or proto-specifier and a substantive / verbal semifinitive. The formal particle in a subject is associated with a strong or super-strong space specifier. In an independent and dependent interrogative sentence, as well as in a dependent narrative one, the fixing of a principal substantive semifinitive is postulated to start with a super-strong specifier. It is proposed that in independent / dependent clauses the use of the formal particle is stipulated by a possible opposition of a fixing verbal semifinitive against the pressure of outer space, as well as by informativity
of an interrogative / conjunctive element. For dependent clauses it is also established that the formal particle in Danish and, sometimes in English, can fill (or accompany) the vacant strong substantive semifinitive and terminate its being vacant; Swedish and Norwegian use for this, instead of the formal particle, an adverbial-substantive unit. Filling the vacant strong substantive semifinitive makes the main sentence parts complete, and a dependent clause becomes more similar to an independent clause. It confirms the statement of the binomiality idea that a narrative and interrogative dependent clause is syntactically «in-between» a narrative independent clause and an interrogative independent clause. Still, the use of the vacant or non-vacant strong substantive semifinitive can be stipulated, like in Danish, by the informativity of the conjunctive element. In case of a high informativity of the conjunctive element the strong substantive
semifinitive may remain vacant.
