: The phrase is a corruption of "for all intents and purposes" by persons who have heard the phrase, but have not read it in it's proper form. It means "for all intents, and for all purposes."
: Taken literally, the phrase means "for purposes which are intense. All purposes which are not intense are not included." This is almost completely opposite to what is meant by most people, and is why it is imperitive that persons use the proper phrase.
For all intensive purposes, everyone gets this phrase wrong.