Condition

It is theoretically possible to fulfil a condition which is given in the if-clause.

Form

if clause	main clause
Simple Past	would + infinitive  or could + infinitive  or might + infinitive

Examples

If I studied,	I would pass the exams.
If I studied,	I could pass the exams.
If I studied,	I might pass the exams.

The if-clause can be at the beginning or at the end of the sentence.

If I studied,	I would pass the exams.
I would pass the exams	if I studied.

It is impossible to fulfil a condition which is given in the if-clause. Form if clause main clause Past Perfect would + have + past participle  or could + have + past participle  or might + have + past participle Examples If I had studied, I would have passed the exams. If I had studied, I could have passed the exams. If I had studied, I might have passed the exams. The if-clause can be at the beginning or at the end of the sentence. If I had studied, I would have passed the exams. I would have passed the exams if I had studied.