For any given activity, I propose the following operational definitions:

Hobbyist

One who pays money to do the activity.

Professional

One who gets paid to do the activity.

Craftsman

One who sweats the smallest of details involving the activity.

Artist

One who transcends the activity and uses the activity as a tool to communicate higher level ideas.

The only two that are mutually exclusive are hobbyist and professional.[foot]Though even this is debatable. One could pay for personal projects while receiving payment for client projects.[/foot] I don't necessarily see them as hierarchical. One very well could be an artist hobbyist. There are numerous aspects of involvement in anything; these are an attempt at classifying those different types of involvement.