Conditional sentences, if-clauses type I, II, III

Conditional sentences are sometimes confusing for learners of English as a second language.

Which type of conditional sentences is it?
Where is the if-clause (e.g. at the beginning or at the end of the conditional sentence)?

There are three types of conditional sentences.

type	condition
I	condition possible to fulfill
II	condition in theory possible to fulfill
III	condition not possible to fulfill (too late)

1. Form

type	if-clause	main clause
I	Simple Present	will-future or (Modal + infinitive)
II	Simple Past	would + infinitive *
III	Past Perfect	would + have + past participle *

Mind the comma after the if clause.

type	Examples
long forms	short/contracted forms
I	+	If I study , I will pass the exam.	If I study , I 'll pass the exam.
I	-	If I study , I will not fail the exam. If I do not study , I will fail the exam.	If I study , I won't fail the exam. If I don't study , I 'll fail the exam.
II	+	If I studied , I would pass the exam.	If I studied , I 'd pass the exam.
II	-	If I studied , I would not fail the exam. If I did not study , I would fail the exam.	If I studied , I wouldn't fail the exam. If I didn't study , I 'd fail the exam.
III	+	If I had studied , I would have passed the exam.	If I 'd studied , I 'd have passed the exam.
III	-	If I had studied , I would not have failed the exam. If I had not studied , I would have failed the exam.	If I 'd studied , I wouldn't have failed the exam. If I hadn't studied , I 'd have failed the exam.

* We can substitute could or might for would ( should , may or must are sometimes possible, too).