What for? Expressing purpose with an infinitive
English commonly expresses an action's purpose with an infinitive: place to and a base verb after the main clause. This part answers What for? by naming the intended aim.
The pattern says that someone does A in order to do B: in the to-clause, we do not repeat the subject or use a modal verb.
main clause + to + base verb
- verb / V —
- A word for an action or state, such as work or be. The pattern determines its form.
- V1 / base form —
- The base verb without to: work, go, be.
- clause —
- A construction with a verb, often with its own subject: when I arrived. A non-finite clause may leave the subject unspoken: to get home.
We took the ferry to see the islands.
We took the ferry to see the islands.
To see the islands answers Why did we take the ferry?
Greta takes the stairs to stay fit.
Greta takes the stairs to stay fit.
A purpose can explain a habit as well as a single action.
Three forms: to, in order to, and so as to
To, in order to, and so as to express the same purpose. The difference is register: to is neutral and most frequent, while in order to and so as to sound more formal and explicit, so they often appear in official texts, letters, and reports.
The longer forms are particularly natural before verbs such as be, have, or know, and when the speaker wants to emphasize an intention. This is not a requirement: plain to is also entirely correct in formal writing.
to / in order to / so as to + base verb
- verb / V —
- A word for an action or state, such as work or be. The pattern determines its form.
- V1 / base form —
- The base verb without to: work, go, be.
Kasia wrote down the address to remember it.
Kasia wrote down the address to remember it.
A neutral version with the simplest purpose marker.
The board met in private in order to discuss the offer.
The board met in private in order to discuss the offer.
A more formal tone, typical of business language.
Ana slowed her speech so as to sound calm.
Ana slowed her speech so as to sound calm.
So as to is another more formal form with the same meaning.
Form: what follows the marker
In these purpose constructions, to, in order to, and so as to are followed by the base verb: no -s, -ing, or past-tense form. The marker does not vary with the main verb's person, number, or tense.
Common mistakes include omitting to after in order or so as (in order buy), adding -ing (to buying), or adding an unnecessary for (for to buy). Preserve the words and their order in in order to and so as to.
marker + base form (to buy, in order to buy, so as to buy)
- V1 / base form —
- The base verb without to: work, go, be.
She stayed in to finish the essay.
She stayed in to finish the essay.
After to, use the base form finish.
He is saving up to rent a studio.
He is saving up to rent a studio.
The main verb's tense does not affect the form after to.
The manager came in at seven in order to have time to set up.
The manager came in at seven in order to have time to set up.
After in order to, use the base form have.
The same subject
In this lesson's basic pattern, the infinitive's performer is the main clause's subject: I went to buy bread means that I went and I intended to buy bread. To clearly identify another performer, use so that + a separate clause. Other constructions may create a different relationship: in I sent Anna to buy bread, Anna will do the buying.
A purpose can sometimes be phrased with a separate subject, such as so that the flat becomes warmer. Check whether you can instead express it as an action by the main clause's subject: He switched on the heater to warm up the flat.
Tomek turned the music down to hear the phone.
Tomek turned the music down to hear the phone.
Tomek will hear the phone, so the performer is the same and the infinitive fits.
Tomek turned the music down so that his neighbours could sleep.
Tomek turned the music down so that his neighbours could sleep.
The neighbors will sleep. So that with an explicit subject clearly identifies a different performer.
I left the door open for the cat to come in.
I left the door open for the cat to come in.
There is also a separate for + participant + to construction, but this rule does not practise it.
Purpose, direction, or a verb + to pattern?
To has several roles. As a preposition, it indicates direction (to the lake); after verbs such as want, need, and hope, the infinitive belongs to the verb's complement pattern; a purpose infinitive answers What for? A sentence can contain two instances of to.
A useful check is to ask What for? If the answer gives the purpose, it is a purpose infinitive and can be replaced by in order to. Otherwise, it may indicate direction or belong to the verb's complement pattern.
We drove to the lake.
We drove to the lake.
To is a preposition of direction.
We drove to the lake to swim.
We drove to the lake to swim.
The first to indicates direction; the second introduces purpose.
We want to swim.
We want to swim.
The infinitive after want does not express purpose; in order to cannot replace it here.
For and to: why not for to?
In the standard purpose pattern, do not add for directly before to: moved to study, not moved for to study. The intention in I went to buy … requires an infinitive; for buying does not replace to buy here. For + -ing has other functions, such as describing an object's use.
For appears in other correct patterns: for + noun (I went to the pharmacy for some plasters) and for + -ing for an object's intended use (This spoon is for stirring tea).
This spoon is for stirring tea.
This spoon is for stirring tea.
For + -ing describes an object's intended use.
I went to the pharmacy for some plasters.
I went to the pharmacy for some plasters.
For + noun names what the person went to obtain.
I went to the pharmacy to buy some plasters.
I went to the pharmacy to buy some plasters.
The purpose of the subject's own action uses an infinitive.
The purpose clause's position
Most often, the purpose follows the main clause without a comma. For emphasis, it can come first; then use a comma after it.
Plain to or in order to commonly begins a sentence; in order to is also natural at the end. With this opening purpose phrase, the main clause's subject is also the performer of the purpose action.
The café buys local flour to keep costs down.
The café buys local flour to keep costs down.
The purpose follows the main clause with no comma.
To keep costs down, the café buys local flour.
To keep costs down, the café buys local flour.
The purpose comes first, followed by a comma.
In order to reach the summit by noon, they started at dawn.
In order to reach the summit by noon, they started at dawn.
The formal marker at the beginning also takes a comma after the purpose phrase.
Purpose in an answer to Why?
You can answer Why? with a short fragment beginning with a purpose marker: To catch the sunrise. There is no need to repeat the subject because the question already identifies it.
The longer in order to is also possible in a short answer, but sounds more formal or solemn. In free speech, vary the markers according to register and use a base verb after each.
Why are you up so early? — To catch the sunrise.
Why are you up so early? — To catch the sunrise.
A short answer fragment with a purpose marker.
Why did Nina take a taxi? — In order to arrive before the doors closed.
Why did Nina take a taxi? — In order to arrive before the doors closed.
The longer form sounds more formal but is correct.
Common mistakes
Incorrect:Kasia moved to Berlin for to study art.
Correct:Kasia moved to Berlin to study art.
In this standard construction, to study expresses the purpose; remove the unnecessary for before to.
Incorrect:I'm calling for asking about the price.
Correct:I'm calling to ask about the price.
For + -ing does not express the purpose of the speaker's action here; use an infinitive.
Incorrect:Nina went to the post office to posting a parcel.
Correct:Nina went to the post office to post a parcel.
The purpose marker to takes a base verb.
Incorrect:He got a loan in order buy a van.
Correct:He got a loan in order to buy a van.
In order requires to here; do not shorten the marker.
Incorrect:We arrived early so as get good seats.
Correct:We arrived early so as to get good seats.
Do not shorten so as to: to is required after as.
Incorrect:The museum stayed open late for attracting more visitors.
Correct:The museum stayed open late to attract more visitors.
The purpose of the museum's action takes an infinitive rather than for + -ing.