Non-Finite Verbs: Gerunds, Infinitives & Participles

Level B1 · Verb Patterns

A finite verb changes to show tense and agrees with its subject: she swims (present tense, third person singular), she swam (past tense). A non-finite verb form does neither — on its own it shows no tense and never agrees with a subject. English builds three non-finite forms from a base verb: the gerund (swimming), which functions as a noun; the infinitive (to swim, or the bare base swim after certain verbs), which fills verb-like slots such as the object of another verb; and the participle (swimming or swum), which functions as an adjective or opens a participle clause. All three can come from the very same base verb, yet they play completely different grammatical roles — knowing which is which is the key to using any of them correctly.

The three forms side by side, with their typical jobs:

The gerund and the present participle are spelled identically, and that overlap is the single most confusing part of the whole system, because the two forms do completely different jobs. In Swimming is my favourite sport, swimming is the subject of the sentence — a gerund, behaving exactly like a noun. In The swimming pool is closed, swimming describes the noun pool — a present participle, behaving like an adjective (a pool for swimming, not a pool that is swimming). In Swimming across the lake, she felt free, swimming opens a participle clause that describes an action alongside the main clause, with no subject of its own. A gerund can be modified like a noun, with a possessive: Her swimming improved this year (see Possessive + Gerund) — a present participle never takes a possessive, because it isn't a noun.

Prepositions are always followed by a gerund, never a to-infinitive — even when the preposition is the word to itself, which produces the single most common non-finite mistake. I look forward to see you is wrong. It must be I look forward to seeing you, because in look forward to, that to is a preposition, not the infinitive marker (compare I want to see you, where to does mark an infinitive). The same trap catches be used to (I'm used to getting up early, not to get up early), object to, and admit to. A second frequent error is choosing the wrong pattern after a fixed verb — I enjoy to swim and I want swimming are both wrong, because enjoy always takes a gerund and want always takes a to-infinitive; see Verb Patterns and Remember, Forget, Stop & Try: -ing vs To + Infinitive for the full lists, including verbs that change meaning depending on which form follows them.

To identify which non-finite form you're looking at, first check whether it shows tense or agrees with a subject — if it doesn't, it's non-finite. Then look at its job in the sentence: -ing acting as a subject, object, or after a preposition is a gerund; to + base verb after a fixed verb like want, decide, or hope is an infinitive. A bare base verb after make, let, or a perception verb like see, hear, watch, or feel is a bare infinitive; and -ing or -ed/irregular forms working as an adjective, or opening a clause with no subject of their own, are participles. For the full depth behind each pattern, see Verb Patterns, Participle Clauses, Possessive + Gerund, Perception Verbs + Object: Infinitive or -ing, Remember, Forget, Stop & Try: -ing vs To + Infinitive, and -ed vs -ing Adjectives.

Practice

Identifying Gerunds, Infinitives & Participles · Choosing the Right Non-Finite Form