When researching the development of a phrase it is usually the origin that is difficult to determine; the spelling and the meaning are generally pretty well established. With 'for (or to) all intents and purposes' it is the other way about. The origin is unambiguous, as the first recorded use was in an Act of Parliament under Henry VIII, in 1546: "to all intents, constructions, and purposes" http://www.phrases.org.uk...
