While I thought the matter had been settled by better people than I, a friend just asked me about graffiti, thus obligating me to write up a bit about it.
In regards to the question of whether or not graffiti is art, my stock response is to ask “is painting art?” This response is not intended to be flippant, rather it indicates my actual view on the matter which is a serious philosophical position.
Contemporary graffiti is, by its nature, a form of painting. After all, the person creating the graffiti (typically) uses the methods and material of painting (although the paint is typically spray paint). As such, specific examples of graffiti would be assessed as art or not art by the same standards by which a painting would be assessed. For example, a crude tagging involving a person spray painting his/her name on the hood of your car would no more be art than it would be for a person to sign his/her name on a canvas using a brush. As another example, if the ghost of da Vinci manifested and grabbed spray paint to create a work on par with Mona Lisa masterfully on the side of a business, then that would have the same status as the Mona Lisa, at least in terms of being art or not. Thus, given that graffiti is essentially painting it follows that it is as much art as painting is or is not. In fact, given that graffiti involves the very same techniques and mediums as “conventional” painting, the burden of proof would seem to be on those who would deny that graffiti is (or more accurately, can be) art while maintaining that painting is art.
One common objection is that graffiti is not art because it is vandalism and hence a criminal act. While it is true that it can be vandalism and a criminal act, these facts would not seem to have a bearing on its status of being art. The mere fact that something is illegal or classified as vandalism hardly seems sufficient to make something fall outside of the realm of art. After all, imagine a state in which music was a criminal act and labeled as a vandalism of the public sound space. It would hardly follow that music would thus cease to be art. As such, this objection fails.
Another common objection is that graffiti is crude or simplistic and hence cannot be considered art. The obvious reply, to steal from Aristotle, is that not all graffiti is to be condemned, just that which is crude or simplistic. After all, music would not be considered non-art simply because some musicians create crude or simplistic music. The same should hold for graffiti as well.
Thus, graffiti is as much art as painting is or is not.