Purpose Clauses

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.

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.

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.

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.

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).

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.

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.

If the main clause is about the present or future, can and will are natural in the purpose clause (formal may is less common, while could sounds softer). If the main clause is in the past and the purpose also belonged to that past time, choose could or would (more formally, might).

If the action and the purpose belong to the past, could or would are natural. If the intention is still relevant or its result is still in the future, can or will are possible after a past verb: I bought a map so that I can find the hotel. A regular Present Simple is also possible after so that: I’ll write it down so that I remember.

If the person carrying out the purpose is the same person who acts, and no modality is needed, an infinitive is enough: to + verb. So that is needed when the purpose has a different actor or when you want to express can or could: there is no place for a modal after an infinitive.

For + person + to can also naturally name a different actor. The choice depends on the sentence: I left a key for Anna to use — “I left a key for Anna to use.” So that with a separate clause allows you to state the possibility directly through can/could.

After so that, the word order is direct: subject, modal, verb. There is no inversion as in a question. After a modal, the verb has no to and no -s ending. You cannot combine so that with an infinitive such as so that to go: either keep to, or build a subordinate clause.

In speech, that is often omitted: it is equally natural to say so you can get in. The more formal option in order that appears in official language, but at this level the main form is so that.

So that often expresses purpose—a desired result—but sometimes it expresses an actual result. Context determines the difference. So + adjective/adverb + that describes degree and a related result: so long that … — “so long that …”. The result does not necessarily have to have happened already: It may be so cold that the lake will freeze — a prediction.

In this lesson, we use so that for purpose. The construction so + adjective/adverb + that has a different structure: you cannot simply insert an adjective into a purpose conjunction. The mere presence of a modal verb is not enough to determine the meaning without context.

Here we practise affirmative purpose. Negative purpose (so that something does not happen) uses the same structure, but its use, as well as so as not to and in order not to, belongs to a separate rule about negative purpose.

In case is not purpose in the same sense: it is a precaution for the possibility that something will happen. Compare: taking an umbrella in case it rains and taking one so that you can stay dry.

Purpose often helps make a request polite: when you ask someone to do something, give a reason so that the request is clear and considerate. Could you send it today so that I can check it? sounds more helpful and gentler than a bare request.

Purpose also answers the question “why?” in conversation, explains a change of plan, and helps with instructions and advice. In each situation, choose the subject of the purpose clause (you, we, they, or a named person) and match the modal to the tense of the main clause.

In these markers, not goes in the middle: so as not to and in order not to. These are four words used as one unit, followed by the base form of the verb, without -ing, -ed, or a second to.

In order not to and so as not to express the same negative purpose, and both can sound more formal than so that. Choose the form according to rhythm and context, not according to a strict scale of formality.

The order to not is also possible, especially for emphasis: in order to not wake anyone. Do not automatically consider it wrong in writing. For the basic pattern here, we use the familiar not to.

If someone else may perform the undesirable action, a clause with its own subject is needed: so that the guests wouldn't hear. The infinitive pattern cannot do this because it has no place for a second subject.

The negative meaning is expressed by the modal verb: wouldn't means that the undesirable event will not happen, while couldn't means that the undesirable action will be impossible. The base form of the verb follows it.

For a purpose relevant at that time in the past, wouldn't/couldn't are natural. For a present or future purpose, use won't/can't. A past action can still have a currently relevant purpose: He wrote it down so that he won’t forget it — “He wrote it down so that he would not forget it.”

After so that, we often use a modal verb. A simple form is also standard, including in the negative: I’ll write it down so that I don’t forget — “I’ll write it down so that I do not forget.” The main practice here focuses on modal forms.

To say “so that nobody would see,” standard English needs only the negative subject nobody/no one: so that nobody would see. Adding not changes the logic and does not express the same intention.

Correct forms are: so that nobody would see, so that no one could read. The negative meaning is already expressed by the subject, while the modal verb remains affirmative.

First ask who exactly must not perform the undesirable action. If it is the same subject as in the main clause, so as not to or in order not to is enough. If it is someone else, a clause with so that is needed.

For a purpose involving the same subject, use so as not to or in order not to; so that works with either the same subject or a different one. Choose the clearest form while preserving the tense and intention.

The phrase not to does not always express purpose. After told, asked, reminded, or advised, it states the content of a command, request, or piece of advice: the teacher asked us not to talk.

Purpose can also be expressed lexically: to avoid + -ing or to prevent. These are separate patterns that do not replace so as not to in this rule, but it is useful to know that they exist.

In everyday speech, negative purpose appears when we explain our own actions: why we spoke quietly, why we left earlier, or why we hid something. Start with the purpose, then check the subject and the tense.

Good writing combines the two patterns: the infinitive for the speaker’s own purpose and a so that clause for another person’s actions. This makes speech sound natural and precise.