The correct phrase is "to all intents and purposes." This phrase dates back to the 1500s and originated in English law, where it was "to all intents, constructions, and purposes." In modern usage, "for all intents and purposes" is also acceptable. The phrase means "for all practical purposes" and is generally used to compare two nonidentical acts or deeds, i.e.,"We've got a few odd things to finish, but to all intents and purposes the job is done." "They redesigned the old model and created something which was to all intents and purposes a brand new car." A shorter equivalent phrase is "in effect."
When used in a strictly legal sense, the wording would be "intent and purposes," as it refers to one's mental attitude/state at the time said action occurred.
A common malapropism is "for all intense and purposes" (also, "for all intensive purposes") a result of the original phrase being misheard and repeated. The word "intense" is used here incorrectly; "intense" is used in English to indicate a degree of intensity, i.e., "As the afternoon passed, the fire grew more intense." Suggestion
It is important to avoid malapropisms as far as possible, as some people take them as a hallmark of ignorance and lack of education. If you have problems with "to all intents and purposes
," bear in mind that in that expression "intents
" is redundant. Use one of the alternatives suggested above.