The phrase for all intensive purposes is a mondegreen. The real phrase is for all intents and purposes, which means in every practical sense.
Examples
Although for all intensive purposes makes no sense, it appears surprisingly often—for example:
It was a questionable call in the 81st minute that for all intensive purposes decided the outcome. [Bleacher Report]
The student was sharing a story with another student about “Amanda” stealing her fake I.D. Slade reassured the audience that he changed the name for all intensive purposes. [The Quinnipiac Chronicle]
Here are a few examples of correct usage of for all intents and purposes:
Northwest Europe is, for all intents and purposes, every bit as rich as America. [Economist]
For all intents and purposes, my opinion most always mirrors that of the average Canadian . . . [Telegraph Journal]
For all intents and purposes, the Nexus One is a T-Mobile phone. [Polyclef Software]
Even when used correctly, for all intents and purposes generally serves no purpose. Each of the above sentences would lose no meaning if the phrase were dropped.
