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Using so that, in order that, if, unless, provided that and similar conjunctions.
Purpose clauses explain the intended aim of an action, while condition clauses state circumstances that must be satisfied for something to happen or be true.
Common purpose structures include so that and in order that, while common condition structures include if, unless, provided that, as long as, and on condition that.
So that can introduce a clause expressing the purpose or intended result of an action.
For example, I left early so that I could catch the train.
So that purpose clauses commonly use can, could, will, would, may, or might to express intended possibility or ability.
For example, She spoke slowly so that everyone could understand her.
In order that introduces a formal purpose clause.
For example, The system was redesigned in order that users could access it more easily.
So that and in order that can both express purpose, but in order that is more formal and less common in everyday English.
For example, We left early so that we could arrive on time is more natural in ordinary conversation than We left early in order that we could arrive on time.
If introduces a condition on which the main clause depends.
For example, If it rains, we will stay home.
Unless introduces a negative condition and is often equivalent to if ... not.
For example, Unless you hurry, you will be late.
Unless and if ... not can often express the same condition, but their meanings should be compared in the context of the whole sentence.
For example, Unless you study, you will fail is similar to If you do not study, you will fail.
Provided that introduces a condition under which something is considered possible, acceptable, or permitted.
For example, You can borrow the car provided that you return it before midnight.
Providing that is an alternative to provided that and introduces a condition.
For example, We can go ahead providing that everyone agrees.
Provided that and providing that have essentially the same conditional meaning, although provided that is generally more established in formal writing.
Both can introduce a requirement or condition for something to happen.
As long as introduces a condition that must continue or be satisfied for the main clause to apply.
For example, You can stay as long as you are quiet.
As long as and provided that can both express conditions, but as long as often emphasizes an ongoing requirement or duration.
For example, You can use the room as long as you keep it clean emphasizes an ongoing condition.
On condition that introduces a formal and explicit condition that must be satisfied.
For example, The agreement will be accepted on condition that all parties sign it.
On the condition that has the same basic meaning as on condition that and emphasizes a specific requirement.
For example, They agreed to help on the condition that the deadline was extended.
In case introduces a precaution taken because a possible future event may occur.
For example, Take an umbrella in case it rains.
In case expresses a precaution taken in anticipation of a possible event, while if states a condition that affects the result.
Compare Take an umbrella in case it rains with If it rains, take an umbrella.
In the event that introduces a formal condition referring to a possible situation.
For example, In the event that the system fails, contact technical support.
Should can introduce a tentative or less likely future condition, especially in formal English.
For example, Should you need any assistance, please contact us.
Were can introduce formal hypothetical conditions, especially with be and unreal situations.
For example, Were I in your position, I would wait.
Had can introduce a formal third conditional clause without if.
For example, Had I known about the problem, I would have acted differently.
Only if expresses a condition that is necessary for the main clause to apply.
For example, We will proceed only if everyone agrees.
Even if introduces a hypothetical condition that does not change the result in the main clause.
For example, Even if it rains, we will go ahead with the event.
If introduces conditions, while whether introduces alternatives or uncertainty about which possibility is true.
For example, If it rains, we will stay home differs from I do not know whether it will rain.
Purpose clauses describe an intended aim, while result clauses describe an actual consequence.
Compare I left early so that I could catch the train with It was so late that I took a taxi.
Purpose can often be expressed with a to-infinitive, in order to, or so as to when the understood subject is appropriate.
For example, I left early to catch the train and She spoke slowly in order to be understood.
So as to expresses purpose and is more formal than a simple to-infinitive.
For example, He whispered so as to avoid waking the baby.
Negative purpose can be expressed with so that ... not, in order not to, or so as not to depending on the structure.
For example, She left quietly so that she would not wake anyone and He spoke quietly in order not to disturb them.
Purpose and condition clauses can appear before the main clause to establish the intended aim or condition before the main information.
For example, So that everyone could understand, she explained the procedure slowly. If you need help, call me.
Choose a purpose or condition expression according to its exact meaning and grammatical pattern.
Common mistakes include confusing in case with if, using unless with an unintended double negative, using provided that as a purpose expression, and using future will unnecessarily in ordinary if-clauses.