1. http://www.xtec.es/~ogodoy/sac/rephrasing/conditionals.htm)
Types 0, 1, 2 & 3
MAIN
IF-CLAUSE MEANING
CLAUSE
General conditions
General laws; things
Simple present Simple present
("Zero" Conditional) that are always true
WILL + V
Possible conditions
(also CAN, MAY, Probable future
Simple present
(1st Conditional) MUST & result
imperatives)
Hypothetical WOULD + V
Imaginary situation
conditions
Simple past (also COULD / in the present or
(2nd Conmditional) MIGHT) future
Impossible WOULD HAVE + pp
conditions Imaginary situation
Past Perfect
(also COULD / in the past
(3rd Conditional) MIGHT)
UNLESS can be used with the meaning "IF ... NOT" in general and possible
conditions only.
Other structures
As long as, providing (or provided that) and on condition: these
expressions mean only if and can be used with the same verb forms as
conditional sentences:
In Spain you can drive a car as long as you are 18
Inversion of subject and verb: this structure is very common in formal
English in conditional sentences with should and the past perfect. When
inversion is used, we omit if:
Had I known about the transport strike, I would have taken my car.
Should you meet Sheila, tell her the meeting has been postponed.