CONDITIONALS - SUMMARY/INTRODUCTION

PRESENT AND FUTURE

if + PRESENT SIMPLE + will, shall
unless + PRESENT SIMPLE + will, shall
even if + PRESENT SIMPLE + will, shall
if + PRESENT SIMPLE + may, might, must, needn´t, ought to, should, can, be able to

if + PRESENT SIMPLE + PRESENT SIMPLE
unless + PRESENT SIMPLE + PRESENT SIMPLE
even if + PRESENT SIMPLE + PRESENT SIMPLE

if + will (STRESSED)
if + will (UNSTRESSED)
if + should
unless + should
even if + should




Examples: 
If I go out tomorrow, I´ll post the letters for you.
If John goes, he will pay the bill.
Bob will learn English if he goes to class.
If Peter goes to New York next week, he will go by air.
If I find your wallet, I´ll let you know
If you don´t forget me, I shan´t forget you.
You won´t catch the bus if you don´t hurry.
If dad doesn´t go out, I´ll talk to him.
If you hurry, we won´t be late for school.

I´ll miss the bus unless I run. = I´ll miss the bus if I don´t run.
I´ll work only if he pays me. = I won´t work unless he pays me.
I´ll come only if he calls me. = I won´t come unless he calls me.

Peter won´t catch the bus even if he runs.
(He will not catch the bus)
Peter won´t catch the bus unless he runs.
(He will catch the bus - if he runs.)
Even if you give me a hundred pounds I won´t tell you.
Even if they hurt me I won´t help them.
Even if they put me in prison I won´t help them.

If you drop this football (this stone/this log) it won´t break.
If you drop this glass (this radio/this camera) it will break.
If you drop this pen it may break.
If you drop this box it might break.

If you go out tonight, you should put a coat on.
If you go out tonight, you must put a coat on.
If you go out tonight, you ought to put a coat on.

If you go out tonight, you may (permission) wear my coat.
If you go out tonight, you can (permission) wear my coat.

If you don´t go out tonight, you needn´t wear a coat.

Can (ability) becomes will be able to
If you study hard, you will be able to speak English very well soon.

If you go out, you must take the umbrella.
If you go out, you should take the umbrella.
If you go out, you ought to take the umbrella.
If you go out, you needn´t take the umbrella.
If you go out, you may take the umbrella.
If you go out, you can take the umbrella.



PAST

if + PAST PERFECT + would have PAST PARTICIPLE
                                     should have PAST PARTICIPLE
                                     could have PAST PARTICIPLE
                                     might have PAST PARTICIPLE

if only + PAST PERFECT + would have PAST PARTICIPLE
if only + PAST PERFECT (exclamation)
even if + PAST PERFECT + would have PAST PARTICIPLE
unless + PAST PERFECT + would have PAST PARTICIPLE
if + PAST PERFECT CONTINUOUS + would have PAST PARTICIPLE
if it hadn´t been for (the fact that)
but for (the fact that)
if + PAST SIMPLE + PAST SIMPLE


NON-PAST

if + PAST + would
if + were + would
if + were to + would
if only + PAST + would
if only + PAST (exclamation)
even if + PAST + would
if it weren´t for (the fact that)
but for (the fact that)


MISCELLANEOUS

as if
suppose / supposing / what if / say

a. if = if it is a fact that
b. if = althought, whereas
c. if in modifying clauses
d. if in short phrases
e. if in fixed expressions 


Source: CONDITIONALS - Longman Elements of English Series - by G. Abbott