A look At Communication, Audience and Purpose

Communication is obviously a social affair one's audience must be remembered whether one is engaging in interpersonal or business communication.

Interpersonal communication as a general concept is the process of sending and receiving information between two or more people. because of this, it may be seen that business communication is a subset of interpersonal communication.
While business communication is clearly articulable as the kind of information sharing that would or should occur in a business atmosphere, interpersonal communication contains within it all forms of multi-person communication. This then includes both business communication and something much less formal like two friends chatting about sports.

Audience is different by definition. You are either talking to someone with whom you are conducting business with or you are talking to someone on a personal level. And the purpose is quite clear as well, you are either engaging a person for a reason that relates directly to the furthering of your and their business goals or you're engaging them to further personal goals.

Tone is the hardest to pin down. Usually for interpersonal communication tone is either light or emotional. Business communication can often require a certain amount of levity in order to put the other person at ease. As a general rule business tone is unemotional and almost mechanical. In the United States it attempts to be pleasant which adds to its seeming lack of emotion.