Who or what is an artist, and what makes an artist a professional? Neither question generates an easy answer but, perhaps, there are ways to approach them.
The United States government has answers for both questions, however the answers contradict each other because different agencies are looking for specific kinds of information. The Census Bureau (whose data on artists is extrapolated by the National Endowment for the Arts), for instance, claims that there are something over 100,000 visual artists in the country. The decennial census asks at what job an individual worked on April 1st, or what career activity occupied the largest portion of that day, and, for statistical purposes, the answer to this determines one's employment area. Someone who painted most of that day is a painter unless the respondent indicates otherwise.
The Internal Revenue Service, on the other hand, does not consider someone a professional artist -- able to deduct art-related expenses from gross income on tax forms -- unless that person made a profit on the sale of his or her work in three out of five years. The government, therefore, may deem someone an artist on one hand but a rank amateur on the other hand.
The art market may or may not provide answers to these questions. Certainly, there are many people who exhibit their artwork in galleries and in other art spaces; a portion of these people sell their work regularly, while others sell occasionally or just enough to cover expenses or sell rarely if ever. Anyone can sell something once, if only to a parent. Somewhere on this continuum one may want to place the idea of being a professional, or even being an artist all all, if it is decided that collectors define what art is through their purchases.
In addition, if sales define an artist or his or her professional standing, where does one place Vincent van Gogh, who only sold one or two paintings during his lifetime but was lionized as a towering figure posthumously? Was van Gogh an amateur in life and a professional in death?
Perhaps, an artist is someone who attains an art degree (a Bachelor or Master of Fine Arts, for example) from an art school or even teaches art privately or at a school. Many artists also belong to professional associations, such as a watercolor society or an artists union, which exist to help members' careers in some fashion. However, the lack of a market for their work may undercut the claims artists may make for themselves, regardless of where they studied or teach and to what groups they belong. Most faculty at art schools would have no other money coming in if they gave up their teaching.
Within that 100,000-plus group that the National Endowment for the Arts has defined, there is a wide spectrum of talents and marketability. Categorizing people in too fine a manner often results in numerous exceptions and contradictions. The 20th century view, first articulated by Marcel Duchamp, is that artists define themselves, with no other external forms of validation required. One might add to this that artists who behave professionally are professionals.
Part of being a professional is understanding, first, the variety of ways to exhibit and sell one's artwork, second, the value of joining an artist membership organization or society, third, what art schools look for in prospective faculty members, and, fourth, what the federal government requires for artists claiming art-related deductions. In fact, a number of profit-less artists have successfully defended their deductions to the IRS on the basis of having made efforts to exhibit and sell their work, belonging to an artist organization, earning an art degree or otherwise taking art classes as well as teaching at an art school. Saving receipts and maintaining good records, these artists have been able to document the extent to which art is their vocation, and this process establishes them as professionals.