A childhood belief about speaking

My Mom always used the phrase "For all intensive purposes" when I was growing up, and (of course) I picked it up too. When I was around 25 years old or so, I learned the correct phrase is "For all intents and purposes". I thought, wow, Mom's been saying it wrong all these years, but I never said anything to her about it. About 5 years later, she was watching Wheel of Fortune, and the puzzle solution was "For all intents and purposes". She said,"Heh! Well I'll be damned! I've been saying it wrong for all these years! " She was around 60 at the time.