Infinitive phrases have a wide range of function within the matrix sentence. They can act as expansions of the verb, and as such they can be either marked or unmarked, either transitive or intransitive; they can replace nouns, and can therefore function as subjects, subjective complements, direct objects, objective complements (either marked or unmarked by to), as objects of prepositions, or appositives; they can function as modifiers of sentences, nouns, verbs, adjectives, and in a sense adverbs. But the outer structure of an infinitive phrase (i.e., its structure within the matrix sentence) is no more important than the inner structure, even though most of the traditional work done on infinitives has been done in reference to the outer structure. This article is therefore concerned with the outer structure only insofar as it relates to the inner structure. As it is concerned to a large extent with functional, rather than formal, relationships, the presentation is informal, since there is some disagreement among transformational linguists as to how functional relationships should be displayed.