Originally used in common American/
English vernacular as 'all intents and purposes' by just barely unintelligent people trying to
sound as if the 'intents and purposes' surrounding them are highly important.
This phrase has since been
changed to 'all intensive purposes' by people who do not listen carefully to the original phrase used in poorly written movies and who have also never seen it in print in equally poorly written books.
Also, the person listening to a speaker who says 'all intensive purposes' is likely to overlook it.
Tanar: Yeah, you're pretty much by best
friend, but for all intensive purposes we'll just call it a tie between you and
Kelsey.
Alyssa: Okay!