Verbs: Nonfinite and finite

Verbs can be divided into finite and nonfinite forms. Finite verbs carry tense. So, past and present tense verb forms are finite. Nonfinite verbs do not carry tense, and do not show agreement with a Subject. Put differently, they are not 'limited' by tense or agreement.

The infinitive form of a verb is nonfinite. It is the form which follows to:

to ask to believe to cry to go

to protect to sing to talk to wish

The nonfinite form is the same as the from the base form. In addition to to-infinitives, there are also bare infinitives, in which to is absent:

• Help me to open the gate! (to-infinitive)
• Help me open the gate! (bare infinitive)

The word to in to-infinitives is called infinitival to or the infinitival particle to. It is different from the preposition to.

In addition to the infinitive, there are two additional nonfinite forms:

• the present participle
• the past participle

For example:

1. The old lady is writing a play.
2. The film was produced in Hollywood.

The verb form writing in (1) is known as the present participle form. It does not agree with the Subject the old lady. If it did, it would be writes as in The old lady writes a play. Instead, the auxiliary verb is agrees with the Subject the old lady. The nonfinite present participle writing is part of a present progressive construction. This is one of the most common uses of the present participle. 

In (2), the verb form produced is called the past participle form. It does not agree with the Subject the film. Instead, the auxiliary verb was is the past tense verb related to the Subject. The nonfinite past participle produced is part of a passive construction. This is one of the most common uses of the past participle.

The -ed inflection on past participles should not be confused with the -ed inflection which is used to indicate the past tense of many verbs. For some verbs the past tense and -ed participle have the same shape (pronunciation and spelling), but the two forms are used in different ways. Compare:

1. He produced the film in Hollywood. (past tense form)
2. The film was produced in Hollywood. (past participle form)

In (1), produced is a past tense form. We could change it to present tense as in the example He produces the film in Hollywood. In (2), the auxiliary verb was is a past tense form, and produced is a past participle. We could not change produced to a present tense form, as in *The film was produces in Hollywood because it would then be ungrammatical.