CONDITIONALS 3

THIRD CONDITIONAL = UNREAL / IMAGINARY PAST
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The construction is:
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IF + verb (past perfect conjugation) =
WOULD/COULD/MIGHT HAVE + past participle verb
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If I'd known you'd bring cookies to the party, I would've brought sth different.
(we both brought cookies)
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Mary could have injured herself if she hadn't been wearing the seat belt.
(she didn't injure herself)
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Jack wouldn't have met his friends if he had stayed home.
(he met his friends)
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If you'd been more careful, you might not have broken the glass.
(you broke the glass)
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Take a look at this interesting explanation with illustrative examples:
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http://www.learnenglish.org.uk/gr_movie/s_3_cond/index.htm
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Take a look at the links below:
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http://web2.uvcs.uvic.ca/elc/StudyZone/410/grammar/3cond1.htm
http://www.better-english.com/grammar/con31.htm
http://www.learn4good.com/languages/evrd_grammar/3rdconditional.php3
http://www.mariposa-services.com/pages/e5cond3_match.htm
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You should remember this kind of conditional indicates sth is IMAGINARY in the past.
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Best wishes,
André