You are correct. For all intents and purposes is the usual form of the phrase meaning in every practical sense. For all intensive purposes is a fairly common eggcorn derived from the original phrase.
You read my mind about "crescent".....I always wondered how calling it "crescent" was acceptable. I know now.
a word or phrase that results from a mishearing or misinterpretation of another, an element of the original being substituted for one that sounds very similar or identical (e.g. tow the line instead of toe the line ).
"in and of itself". What's wrong with "by itself"? Oh yeah, I forgot, the very first person who said the former did so because he/she loved the sound of his/her voice.
Oh! Thanks. As in, "Tow that marge; lift that bale." Well, if you've seen the size of Marge lately....
You make a valid point. While redundancy is often annoying, it can be used for emphasis. 8/2/16- Update- today I read a reference to an "offensive insult".
But I believe that would presume that "in" and "of" have the same meaning. For instance, a mom yells at her child "I want you to come OF this house, right now! Sounds silly doesn't it?
"Check surrounding area for safety" My car's rear camera display this message. Wouldn't it be better to check the area for obstructions like children and domestic animals?
