type

"if" clauses

main clauses

condition possible

Simple Present

will + future

condition in theory possible

Simple Past

would + Infinitive
(Conditional)

condition not possible

Past Perfect

would + have + past participle
(Conditional Perfect)

type

example

condition possible

positive

If I learn, I' ll pass the exam.am.

negative

If I learn, I won't fail the exam.

condition in theory possible

positive

If I learned, I would pass the exam.

negative

If I learned, I wouldn't fail the exam.

condition not possible

positive

If I had learned, I would have passed the exam.

negative

If I had learned, I wouldn't have failed the exam.