stylistic:tone, information:classification
to -infinitive clauses

Some modern theories of syntax take many to -infinitives to be constitutive of non-finite clauses. This stance is supported by the clear predicate status of many to -infinitives. It is challenged, however, by the fact that to -infinitives do not take an overt subject, e.g.

The to -infinitives to consider and to explain clearly qualify as predicates (because they can be negated). They do not, however, take overt subjects. The subjects she and he are dependents of the matrix verbs refuses and attempted, respectively, not of the to -infinitives. Data like these are often addressed in terms of control. The matrix predicates refuses and attempted are control verbs; they control the embedded predicates consider and explain, which means they determine which of their arguments serves as the subject argument of the embedded predicate. Some theories of syntax posit the null subject PRO (i.e. pronoun) to help address the facts of control constructions, e.g.

With the presence of PRO as a null subject, to -infinitives can be construed as complete clauses, since both subject and predicate are present.

PRO-theory is particular to one tradition in the study of syntax and grammar (Government and Binding Theory, Minimalist Program). Other theories of syntax and grammar (e.g. Head-Driven Phrase Structure Grammar, Construction Grammar, dependency grammar) reject the presence of null elements such as PRO, which means they are likely to reject the stance that to -infinitives constitute clauses.