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When I first started teaching English, infinitives were one of the hardest concepts to explain — my students would nod, then immediately forget the difference between “to study” and “studying”. The problem wasn’t their attention; it was that infinitives do so many jobs in English. They act as nouns, modifiers, and expressions of purpose all at once. Once I found a way to break that down, everything clicked for my learners, and it can for you too.
I’ll walk you through what infinitives actually are, the four different types you need to know, how they function in sentences, and exactly where learners go wrong. You’ll also find a conjugation table, side-by-side comparisons with gerunds, and practice examples that you can use immediately.
Key Takeaways
- An infinitive is “to” + base verb — to run, to speak, to learn. It’s a non-finite form (no tense of its own).
- Four main types exist — full, bare, split, and infinitive phrases; each has different rules and uses.
- Infinitives function as multiple parts of speech — they can be nouns, adjectives, or adverbs depending on context.
- Modal verbs change the rule — after can, should, will, must, use bare infinitives (no “to”).
- Learn the contrast — infinitives and gerunds both act as nouns, but they follow different verbs and convey different meanings.
What Is an Infinitive?
An infinitive is the base form of a verb preceded by the word “to”. It’s called a non-finite verb because it doesn’t carry a tense by itself — it doesn’t tell you whether the action is happening now, happened before, or will happen later.
Examples of infinitives: to run, to eat, to sleep, to speak, to understand, to be, to go
The “to” is sometimes called the infinitive marker or infinitive particle. It shows that the verb form is being used as an infinitive, not as the main verb of a clause.
What Infinitives Are Not
Infinitives are NOT the same as:
- Gerunds — the “-ing” form (running, eating, sleeping). Both can function as nouns, but they’re different forms.
- Present tense verbs — “I run every morning” is present tense. “I want to run” contains an infinitive.
- Imperatives — commands like “Run!” Use the base form without “to”, but they’re not infinitives.
The Four Types of Infinitives
1. Full Infinitives
A full infinitive is the base form of a verb with “to” attached. This is the most common type and the one you’ll encounter most often.
Structure: to + base verb
Examples:
✓ I want to learn English.
✓ She needs to finish her homework.
✓ They plan to travel to France next year.
✓ He promised to call me at 7 pm.
Full infinitives follow most action verbs and many other verb patterns. They’re the safest choice when you’re unsure.
2. Bare Infinitives
A bare infinitive is the base form of a verb without “to”. These are used after modal verbs and a few special verbs.
Structure: base verb (no “to”)
After modal verbs (can, could, may, might, shall, should, will, would, must):
✓ She can swim. (not “can to swim”)
✓ He should study more. (not “should to study”)
✓ They will arrive tomorrow. (not “will to arrive”)
✓ I might go to the party. (not “might to go”)
After certain verbs (let, make, help, see, hear, watch, feel, notice, observe):
✓ Let me go. (not “let me to go”)
✓ She made him work. (not “made him to work”)
✓ I saw her run across the street. (not “saw her to run”)
Key Rule: After modal verbs and verbs of perception, drop the “to”. After regular infinitive verbs, keep the “to”.
3. Split Infinitives
A split infinitive occurs when an adverb (or other word) is placed between “to” and the base verb. While once considered a serious grammar error, modern English is more forgiving.
Structure: to + adverb + base verb
Examples:
He decided to carefully read the instructions.
She wants to slowly improve her skills.
They plan to secretly donate to charity.
Traditional advice: Rewrite to avoid the split.
He decided to read the instructions carefully.
She wants to improve her skills slowly.
Modern view: Split infinitives are acceptable in casual writing and speech, but formal or academic writing should avoid them when possible.
4. Infinitive Phrases
An infinitive phrase is an infinitive along with its objects, modifiers, or complements. The entire phrase functions as a single unit.
Structure: to + verb + (object/modifier)
Examples:
To succeed in life, you need discipline and patience. (infinitive phrase as subject)
She wants to study medicine at a top university. (infinitive phrase as object)
The best way to learn is by practicing every day. (infinitive phrase as complement)
To finish this project on time, we must work together. (infinitive phrase showing purpose)
How Infinitives Function in Sentences
Infinitives as Nouns (Nominal Function)
Infinitives can act as nouns — they can be subjects, objects, or complements of sentences.
As a subject:
To swim is my favorite activity. (The infinitive phrase is the subject.)
To travel the world has always been my dream.
To forgive is divine.
Note: Sentences starting with infinitive subjects often sound formal. In casual speech, we use “it”: “It is my favorite activity to swim.”
As a direct object (after certain verbs):
She wants to learn guitar. (The infinitive is what she wants.)
I need to finish this project.
He hopes to graduate next year.
As a subject complement (after linking verbs):
My goal is to become a teacher.
The best thing is to spend time with family.
Infinitives as Adjectives (Adjectival Function)
Infinitives can modify nouns, functioning as adjectives. They typically come immediately after the noun they modify.
Examples:
I need a book to read. (The infinitive “to read” modifies “book”.)
She’s looking for a place to live.
He found a job to support his family.
They need time to think.
In these sentences, the infinitive answers the question “What is the noun for?” or “What will be done with the noun?”
Infinitives as Adverbs (Adverbial Function)
Infinitives can also function as adverbs, modifying verbs and showing purpose, reason, or result.
Showing purpose (answering “Why?”):
I went to the store to buy milk. (Why did you go? To buy milk.)
She studied hard to pass the exam.
He exercises daily to stay healthy.
Showing result or cause:
She was surprised to see him there.
They were happy to hear the good news.
Conjugation Reference: Infinitive Forms Across Tenses
| Tense / Form | Example (with verb “to go”) | Use |
|---|---|---|
| Present Infinitive | to go | Most common; refers to the general action |
| Present Progressive Infinitive | to be going | Action in progress at a future time |
| Perfect Infinitive | to have gone | Action completed before the main verb |
| Perfect Progressive Infinitive | to have been going | Ongoing action completed before the main verb |
Examples in context:
I want to go to Paris. (present infinitive — simple, future action)
She seems to be struggling with the assignment. (progressive — current difficulty)
He claims to have visited 50 countries. (perfect — action in his past)
They appear to have been waiting for hours. (perfect progressive — long-duration past action)
Common Mistakes with Infinitives
Mistake 1: Using “to” After Modal Verbs
✗ Incorrect: She can to swim very well.
✓ Correct: She can swim very well.
Explanation: Modal verbs (can, should, will, must, may, might) are always followed by bare infinitives — no “to”.
✗ Incorrect: They should to arrive by 5 pm.
✓ Correct: They should arrive by 5 pm.
Mistake 2: Dangling Infinitive Modifiers
✗ Incorrect: To improve your English, television helps a lot.
Problem: The subject of the sentence (“television”) is not the one performing the action in the infinitive (“to improve”). The infinitive is “dangling” — it doesn’t have a clear subject.
✓ Correct: To improve your English, watch television often.
Explanation: Now the understood subject of the infinitive (you) matches the subject of the main clause.
✗ Incorrect: To finish on time, the instructions must be followed carefully.
✓ Correct: To finish on time, follow the instructions carefully.
Mistake 3: Mixing Infinitives and Gerunds
✗ Incorrect: She enjoys to read books.
✓ Correct: She enjoys reading books.
Explanation: “Enjoy” is a gerund verb; it’s followed by “-ing” forms, not infinitives.
✗ Incorrect: I avoid to eat spicy food.
✓ Correct: I avoid eating spicy food.
Mistake 4: Forgetting “to” with Infinitive Verbs
✗ Incorrect: He wants go to the beach.
✓ Correct: He wants to go to the beach.
✗ Incorrect: I decided leave early.
✓ Correct: I decided to leave early.
Watch Out: The difference between “to” the preposition and “to” the infinitive marker can confuse learners. In “I go to school,” “to” is a preposition. In “I want to go,” “to” marks an infinitive. Context tells you which is which.
Infinitives vs. Gerunds — A Clear Comparison
Both infinitives and gerunds can function as nouns, but they’re different forms and follow different verbs.
| Feature | Infinitives | Gerunds |
|---|---|---|
| Form | to + base verb | verb + -ing |
| Function | Noun, adjective, or adverb | Noun only |
| After verbs of intention/desire | ✓ Yes (want, plan, hope, decide) | ✗ No |
| After verbs of enjoyment | ✗ No | ✓ Yes (enjoy, like, love, hate) |
| After prepositions | ✗ No (rare) | ✓ Yes (before, after, by, in) |
| Can be a subject? | ✓ Yes (To read is fun.) | ✓ Yes (Reading is fun.) |
| Can be an object? | ✓ Yes (I want to read.) | ✓ Yes (I enjoy reading.) |
| Sample sentence | I want to learn Spanish. | I enjoy learning Spanish. |
How the Choice Changes Meaning
Infinitive: I like to cook. (I enjoy cooking as a general activity or habit.)
Gerund: I like cooking. (Same meaning in modern English; the infinitive sounds slightly more formal.)
Infinitive: She stopped to talk to her friend. (She paused what she was doing in order to talk.)
Gerund: She stopped talking to her friend. (She ended the conversation.)
Infinitive: He remembers to lock the door. (He recalls the action; he does it.) — This is a future or intentional action.
Gerund: He remembers locking the door. (He recalls doing it in the past.)
Infinitives in Dialogue
Emma: What do you want to do this weekend?
James: I’m hoping to finish my project, but I’d love to go hiking if we have time.
Emma: To be honest, I’m tired of staying indoors. I need to get outside and breathe fresh air.
James: Then let’s plan to go on Saturday morning. We can bring snacks to enjoy while we walk.
Emma: That sounds perfect! Do you remember to bring your camera? The mountain views are beautiful in spring.
James: Of course. I’m eager to capture some great photos. Should we invite our friends too?
Emma: Yes, let me text them and ask if they want to join us!
Quick Quiz
Choose the correct form (infinitive or gerund) or identify the infinitive type:
- She wants _____ (to study / studying) medicine in college.
- He enjoys _____ (to read / reading) mystery novels.
- You should _____ (to finish / finish) your work before lunch.
- My goal is _____ (to become / becoming) a professional musician.
- “To boldly go where no one has gone before” — what type of infinitive is “to boldly go”?
Answers: 1. to study (infinitive verb) · 2. reading (gerund verb) · 3. finish (bare infinitive after modal “should”) · 4. to become (infinitive as subject complement) · 5. split infinitive
Related Articles
- ↑ Master Pillar: English Grammar
- Verbs Followed by Infinitives — a complete list of 50+ verbs
- ↑ Back to pillar: English Verbs (Pillar)
Frequently Asked Questions
What is the definition of an infinitive?
An infinitive is the base form of a verb preceded by “to” — for example, “to run,” “to eat,” “to learn.” It’s called non-finite because it doesn’t have tense. Infinitives can function as nouns, adjectives, or adverbs in sentences.
What are the four types of infinitives?
The four types are: (1) Full infinitives — “to” + base verb (to go); (2) Bare infinitives — base verb without “to” (go), used after modals; (3) Split infinitives — “to” + adverb + verb (to quickly go); (4) Infinitive phrases — infinitive with objects or modifiers (to study medicine).
Can an infinitive be both a noun and an adjective?
Yes. The same infinitive can have different functions in different sentences. For example, in “To read is fun,” the infinitive is a noun (subject). In “I need a book to read,” it’s an adjective (modifying “book”).
What is the difference between a bare infinitive and a full infinitive?
A full infinitive has “to” (to run), while a bare infinitive doesn’t (run). Bare infinitives appear after modal verbs (can, should, will, must) and certain other verbs (let, make, see, hear). Full infinitives are more common and follow most action verbs.
Are split infinitives always wrong?
No. Split infinitives (like “to boldly go”) were once considered serious errors, but modern English is more forgiving. However, formal and academic writing should still avoid them when possible. In casual writing and speech, they’re acceptable.
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