Conditionals.

1. First conditional. (Also, "real conditional".)
..... a. IF present, future
..... b. IF present, imperative (Called "zero conditional" in some books.)
..... c. IF present, present (Called "zero conditional" in some books.)
Variant 1 of the first conditional for subtypes a and b.
......... IF ... SHOULD plain-form, ...
Variant 2 of the first conditional for subtypes a and b.
......... SHOULD ... plain-form, ... (no IF)

2. Second conditional. (Also, "unreal conditional", "hypothetical conditional")
..... IF past, WOULD plain-form
......... 2a. Change of 'was' to 'were' when the past is 'was'.
......... 2b. No change of 'was' to 'were' when the past is 'was'.
Variant 1 of the second conditional.
......... IF ... WERE TO plain-form, WOULD plain-form
Variant 2 of the second conditional.
......... WERE ... TO plain-form, WOULD plain-form (no IF)

3. Third conditional. (Also, "past unreal conditional", "counterfactual")
..... IF past perfect, WOULD HAVE past-participle ...
Variant 1 of the third conditional.
..... HAD [subject] past participle, WOULD HAVE past-participle ... (no IF)
Variant 2 of the third conditional.
..... IF ... WERE TO HAVE past-participle, WOULD HAVE past-participle ...
Variant 3 of the third conditional.
..... WERE ... to HAVE past-participle, WOULD HAVE past-participle ... (no IF)


Variants are used much less often than the basic forms shown above.


Mixed conditional. Any combination of an IF clause above from one type of conditional and a main clause above from a different type of conditional.


Note: Variants of any of the above can be formed by substituting another modal verb for WILL or WOULD.
...... CAN, MAY, and MIGHT can substitute for WILL.
...... COULD and MIGHT can substitute for WOULD
...... COULD HAVE and MIGHT HAVE can substitute for WOULD HAVE.

CJ

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