Purpose as a separate subordinate clause
Sometimes you need to say not simply “why I am doing this,” but “why this is for someone else” or “what this will allow someone to do.” Then put so that after the main clause and build a complete subordinate clause: its own subject, a modal verb, and the base form of the main verb.
The modal expresses the possibility created by the action: can and could express ability, while will and would express an expected result. This is what distinguishes a subordinate purpose clause from a simple infinitive, which has neither a separate subject nor a modal.
... + so that + subject + can / will / could / would + verb without to
- subject / S —
- The grammatical subject: who or what the clause is about; the verb agrees with it. In The book was written, the book is the subject, although someone else does the action.
- verb / V —
- A word for an action or state, such as work or be. The pattern determines its form.
We booked a larger room so that all the volunteers could sit together.
We booked a larger room so that all the volunteers could sit together.
The subject of the purpose clause is all the volunteers, not we; could adds the idea of possibility.
I'll write the steps on the board so that the new students can copy them.
I'll write the steps on the board so that the new students can copy them.
The main clause is about the future, so the purpose clause uses can.
The modal depends on the tense of the main clause
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.
Dina is saving money so that her sister can study abroad.
Dina is saving money so that her sister can study abroad.
The main clause is in the present: the purpose clause uses can.
Dina saved money so that her sister could study abroad.
Dina saved money so that her sister could study abroad.
The main clause is in the past: the purpose clause uses could.
So that or to + infinitive
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.
Nick came early to help us.
Nick came early to help us.
The actor is the same, and no modality is needed: an infinitive is enough.
Nick came early so that we could start on time.
Nick came early so that we could start on time.
The purpose concerns other people (we), so a subordinate clause with could is needed.
Structure: word order and common pitfalls
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.
The speaker repeated the date so that everybody could note it down.
The speaker repeated the date so that everybody could note it down.
The subject everybody comes before could; after could, use note without to.
I'll text you the code so you can get in.
I'll text you the code so you can get in.
Conversational form: that is omitted, but the purpose-clause structure is the same.
Purpose or result
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.
We left early so that we could avoid the queue.
We left early so that we could avoid the queue.
Purpose: the action was performed for the sake of a future result.
The queue was so long that we left.
The queue was so long that we left.
Result: an adjective stands between so and that, and the result has already occurred.
Scope of the topic: what we are not learning here
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.
I took an umbrella in case it rained.
I took an umbrella in case it rained.
In case expresses a precaution: it might rain, but it is not certain.
I took an umbrella so that I could stay dry.
I took an umbrella so that I could stay dry.
So that expresses purpose: the umbrella is needed specifically for this.
Purpose in communication: notes, requests, and explanations
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.
Could you share the file now so that we can all see the numbers?
Could you share the file now so that we can all see the numbers?
A request with a purpose: it politely explains why the file is needed.
I changed the time so that everyone could come.
I changed the time so that everyone could come.
An answer to “why?” in the past: could.
Common mistakes
Incorrect:I'll send you the link so that to join the meeting.
Correct:I'll send you the link so that you can join the meeting.
After so that, a subordinate clause with a subject and a modal is required, not an infinitive with to.
Incorrect:Please speak slowly so that I can to understand you.
Correct:Please speak slowly so that I can understand you.
After the modal can, the verb is used without to.
Incorrect:I'll leave the keys here so that can you get in.
Correct:I'll leave the keys here so that you can get in.
After so that, the word order is direct: the subject comes before the modal; there is no inversion.
Incorrect:The film was so long so that we missed the last bus.
Correct:The film was so long that we missed the last bus.
In the result construction, after so + adjective, use only that, without a second so.