tag:blogger.com,1999:blog-7701757403364514168.post8847794465747160658..comments2009-05-06T11:45:42.169-04:00joshhttp://www.blogger.com/profile/12809501199806590382noreply@blogger.comBlogger1125tag:blogger.com,1999:blog-7701757403364514168.post-56845585014014340362009-05-06T11:45:00.000-04:002009-05-06T11:45:00.000-04:00If and only if (iff) is distinct from simple if even in our intuitions. Iff implies that for no other reason would the consequent (the then clause) be true. Simple if only indicates one way the consequent could happen. To clarify, I'll use your example.<br /><br />"If you mow the lawn, I'll give you $5."<br /><br />If you mowed the lawn, I can safely say you were given $5. But if you were given $5, I could suspect but not be certain that you mowed the lawn.<br /><br />"If and only if you mow the lawn, I'll give you $5."<br /><br />If you were given $5, I can know for certain that you mowed the lawn: If the proposition is true, then for no other reason would you have been given $5. (Note that "iff the proposition is true" would be innapropriate because several antecedents (if clauses) could have that very consequent.)Anonymousnoreply@blogger.com