In the sentence, "He loves to travel," "to travel" is described as a nonfinite clause (source). However, one of the rules regarding clauses is that they must at least contain a subject and a verb. So how can "to travel" be a clause? Or is the subject of "to travel" implied? And, why isn't "to travel" a prepositional phrase?

  • Most non-finite clauses are subjectless, though the subject is usually retrievable form the matrix clause. The non-finite clause in your example is no exception: it is subjectless, but it's clear that it is "he" (or more precisely the referent of "he") who loves something, and since it is the travelling that is loved, the subject of the subordinate non-finite clause can only be "he". Why do you think that "to travel" is a prep phrase?
    – BillJ
    Commented Apr 24, 2016 at 17:18
  • It is not a propositional phrase for this obvious reason.A prepositional phrase will function as an adjective or adverb. As an adjective, the prepositional phrase will answer the question Which one? As an adverb, a prepositional phrase will answer questions such as How? When? or Where?
    – Mia
    Commented Apr 24, 2016 at 17:26
  • 1
    What @BillJ said. My references are annoyingly imprecise about the definitions of phrase and clause, preferring to define by example. I think some modern grammars prefer to define nonfinite expressions as clauses because non-finite verbs often take subjects and objects. Any missing subjects have to be classified as "unstated" or "retrievable." After all, imperative clauses, which are finite, also have missing subjects.
    – deadrat
    Commented Apr 24, 2016 at 17:35
  • @Mia The reason that an infinitive is not a prepositional phrase is that prepositional phrases require a noun phrase to follow the preposition, and for infinitives, it's a verb that follows to. Prepositional phrases can function as complements (He is at the office.), and prepositions like despite (He left despite her objections.) are hard classify with how, when, and where.
    – deadrat
    Commented Apr 24, 2016 at 17:45
  • Did you think that "to" might be a preposition and therefore "to travel" a preposition phrase?
    – BillJ
    Commented Apr 24, 2016 at 17:45

3 Answers 3


As you note, a clause is defined as a group of words with a subject and a predicate, but it's argued that infinitives, as in your examples, can function as clauses by taking nonovert subjects. From the Wikipedia article on clauses

"Some modern theories of syntax take many to-infinitives to be constitutive of non-finite clauses.[5] 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.

She refuses to consider the issue. He attempted to explain his concerns.

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. She refuses PRO to consider the issue. He attempted PRO to explain his concerns. With the presence of PRO as a null subject, to-infinitives can be construed as complete clauses, since both subject and predicate are present."

Apparently not everyone agrees with this syntactical prestidigitation.

"One must keep in mind, though, that 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."

  • But whether infinitives are called "clauses" or not is simply a matter of terminology, isn't it? Call it a clause, call it something else -- What's the difference? (So long we're clear about how the term "clause" is being used.)
    – Greg Lee
    Commented Apr 24, 2016 at 17:45
  • To-infinitivals can take an overt subject: For them to refuse you a visa was quite outrageous
    – BillJ
    Commented Apr 24, 2016 at 17:49
  • @BillJ, "them" in your example is not a subject. If it were, it would have the subject form "they", and the verb could agree with it in number.
    – Greg Lee
    Commented Apr 24, 2016 at 18:14
  • @Greg Lee In to-infinitivals, a personal pronoun with a nominative-accusative contrast takes accusative form, cf. all I want is [for us to be reunited, and clause subjects take singular agreement.
    – BillJ
    Commented Apr 24, 2016 at 18:19

As you suggest, the logical subject of the verb "travel" is "he". And the fact that "travel" is a verb is one reason why "to travel" cannot be a prepositional phrase. PP have a preposition and a NP (noun phrase).

Since ordinarily only expressions of the same grammatical category can be coordinated with "and", we can construct examples to test whether "to travel" could be a PP with a P and a NP:

*He loves to travel and in the kitchen. (so "to travel" is not a PP)  
*He loves to travel and the kitchen. (so "travel" is not a NP)  
*He loves to and in travel.  (so "to" is not a P)

By definition,A nonfinite clause cannot stand on its own. It rarely includes a subject, and the verb cannot be inflected for tense or person. A nonfinite clause may serve as a subject or a complement to a verb, a preposition or a noun. Here are some examples:


To speak in class is difficult for some children. (subject)

Speaking in class is what he does best. (subject)

Verb complement:

He loves to participate. (verb complement)

He dislikes sitting quietly. (verb complement)

Prep complement:

Charlie smiled after answering the question. (prep complement)

Charlie is used to answering questions.

Charlie is interested in hearing the answers.

Noun complement:

Prepared students excel in class. (modifier to subject noun)

Students encouraged by their teachers do well. (modifier to subject noun)

Now back to your question:

He loves to travel. ( verb complement)

For more information,you can follow the links below:



  • All this is mostly true. But some finite clauses can't stand on their own, and some don't contain explicit subjects. And noun phrases may serve as subjects and complements. The OP's question is why non-finite constructions are classified as clauses and not phrases.
    – deadrat
    Commented Apr 24, 2016 at 17:51

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