Infinitive phrases as subjects or objects

In “To finish the project early requires planning,” the words to finish the project early form an infinitive phrase that acts as the subject. In “The team hopes to finish the project early,” the same kind of phrase acts as the object of hopes. Recognizing the phrase as a unit helps with both meaning and sentence structure.

Infinitive phrase as subject

An infinitive phrase can name an action that functions as the subject of a sentence: “To compare the sources takes time.” The entire phrase is singular for agreement purposes, even though the phrase may contain a plural noun. In formal prose, writers sometimes move a long infinitive phrase to the end and use it as a placeholder subject: “It takes time to compare the sources.”

Infinitive phrase as object

A phrase can complete the meaning of a verb as a direct object: “The candidate plans to review the outline.” Here, to review the outline is what the candidate plans. Some verbs take infinitives naturally, while others take gerunds or allow both with a change in meaning. On an editing question, determine what grammatical role the phrase plays rather than assuming every to-verb phrase is an object.

Other functions

An infinitive phrase can also be a subject complement (“Her goal is to improve”), an adjective modifying a noun (“the best route to take”), or an adverb expressing purpose (“She arrived early to prepare”). The phrase’s position alone does not determine its function; identify the word it modifies or the role it fills in the clause.

Do not confuse infinitives with prepositional phrases

The word to can introduce either an infinitive or a prepositional phrase. In “to study,” to precedes a base-form verb and marks an infinitive. In “to the library,” to is a preposition followed by a noun phrase. This distinction helps when analyzing sentence structure and punctuation.

Quick identification method

1. Find to followed by a base-form verb, or identify a bare infinitive after a verb such as make or let.
2. Include objects and modifiers that belong to that verb.
3. Ask whether the whole phrase names the subject, completes a verb, describes a noun, or explains purpose.
4. Check agreement and punctuation based on the phrase’s role.

For exam questions, treat the infinitive phrase as a unit, then determine its job. The phrase may be noun-like, adjective-like, or adverb-like; its function comes from its relationship to the rest of the sentence.

Recognize the infinitive and its job

An infinitive is the base form of a verb, usually preceded by to: to read, to calculate, to explain. The whole infinitive phrase can function as a noun, adjective, or adverb. In “To compare both plans takes time,” the phrase to compare both plans is the subject. In “She hopes to pass,” it completes the meaning of hopes. In “He studied to improve his score,” it explains why he studied. The word to may also be a preposition, as in “walked to class,” so check whether a verb follows it.

A useful test is to ask what role the phrase plays in the sentence. If it names an action or goal, it may act as a noun. If it modifies a noun, it often acts adjectivally: “a rule to remember.” If it modifies a verb or adjective by explaining purpose or extent, it may act adverbially: “ready to begin” or “paused to check.” Some school grammars use slightly different labels for borderline cases; the important point is how the phrase relates to surrounding words.

Keep the subject and verb aligned

When an infinitive phrase is the subject, it usually takes a singular verb because the phrase names one action or idea: “To arrive early is helpful.” A plural noun inside the phrase does not control the main verb: “To review the pages and complete the exercises takes two hours.” The full infinitive phrase is the subject. Writers sometimes recast it as a gerund phrase—“Reviewing the pages and completing the exercises take two hours”—where the compound subject can take a plural verb.

Place modifiers beside the infinitive they explain

An infinitive can be modified by an adverb: “to answer carefully.” Avoid placing a modifier so far away that readers might attach it to the wrong action. “She planned to quickly review the outline” splits to from the verb; this split infinitive is accepted by many modern style guides when it improves clarity. Traditional editing exercises may prefer “planned quickly to review” or “planned to review quickly.” Choose a revision that keeps the intended emphasis and does not create ambiguity.

A dangling infinitive phrase can also assign an action to the wrong person: “To finish on time, the questions were answered quickly” makes it sound as though the questions are trying to finish. Put the actor next to the phrase: “To finish on time, the candidates answered the questions quickly.” Check who is meant to perform the infinitive’s action.

Distinguish infinitives from participles and gerunds

In “To study is useful,” to study is an infinitive. In “Studying is useful,” studying is a gerund functioning as a noun. In “The studying candidate took notes,” studying is a participle modifying candidate. These forms can look similar, but their function differs. For editing, locate the whole phrase and identify its role rather than classifying a word by its ending alone.

• Find to plus a base verb; distinguish it from to used as a preposition.
• Identify whether the full phrase names, modifies, or completes an idea.
• Treat an infinitive phrase as a singular subject in standard agreement questions.
• Place the actor next to purpose phrases to avoid dangling modifiers.
• Check the function of -ing forms before calling them gerunds.

Use the concept in a question

An infinitive is to plus the base form of a verb, such as to read or to compare. Its phrase can function as a noun: “To revise carefully takes time” uses the infinitive phrase as the subject; “The class learned to revise carefully” uses it as the object of learned. It can also modify a noun or explain purpose, so identify its role in the whole sentence rather than labeling every to phrase a noun. Compare “to the library,” where to is a preposition followed by a noun, not an infinitive. This distinction matters in grammar questions about sentence function and parallel structure.