The phrase "for all intents and purposes" seems redundant and circular to me, because of the overlap of the meanings of the individual words:
intend: have in mind as what one wishes to do or achieve.
purpose: intended result of effort.
The thing that one wishes to do or achieve is the intended result of the effort. Thus saying the same thing twice. Is this done for emphasis as in the phrase "last and final call"?
Best Answer
Emphasis as you say, and also for a sense of completeness and covering all cases; should there be any doubt as to whether something could perhaps be only considered an intent or only a purpose then it's clearly included in the phrase!
Such doubling up is common in older English idioms ("wrack and ruin") especially in legal phrases ("cease and desist", "aid and abet") and some which originate from legal contexts and have since acquired a more colloquial meaning ("all and sundry").
It's been suggested that the origin is in the tendency to once double up charges, demands and other important points of legal business with both the Anglo Saxon and the Norman, and that this remained after the English merged on the common language of Middle English. There would also be legal terms in Latin being sometimes translated and sometimes not. However, many of the words in such expressions are of the same origin, rather than one being Old English and the other Norman French.