The expression to all intents and purposes started life as legalese in 1546 when it appeared in an Act of Henry VIII: “to all intents, constructions, and purposes.” The expression means “in regard to any end or object, for all practical purposes, practically” For example: Now that the plaintiff has been satisfied, the case is closed to all intents, constructions, and purposes.
The phrase migrated from legal jargon to popular usage:
Whoever resides in the World without having any Business in it..is to me a Dead Man to all Intents and Purposes –Addison, 1709
The materials are so hardened and knit together that to all intents and purposes they form one solid mass. –Ruskin, 1856
In the 19th century, the preposition “to” began to give way to “for”:
The rest of the nation consists, for all intents and purposes, of one immense class. –Matthew Arnold, 1879.
It remained for speakers and writers of the 20th and 21st centuries to mishear this strongly-embedded cliché as “for all intensive purposes.”
Internet marketing site:
We’ve tested this extensively, and eventually you will disappear or go so far down the SERPs that for all intensive purposes you will not exist anyway if you do that.
Soap opera fan site:
The only family who seems like a family these days (no pun intended) is the Kiriakis bunch. Victor has Bo, Philip, Justin, and Brady. Not to mention Daniel who for all intensive purposes feels like a Kiriakis.
Amazon reviewer commenting on a book called A Concise Economic History of the World: From Paleolithic Times to the Present:
the title is … for all intensive purposes incorrect.
For all intents and purposes is a cliché that careful writers will avoid.
“For all intensive purposes” is not even an option.