The question of what is prior art involves at least four different dimensions. The first is the dimension of time. When does art become prior ? When, if ever, is it too old and forgotten to be considered prior art? The second is the dimension of place. The patent statutes make both United States and foreign patents and publications prior art, but limit knowledge, use, and invention to in this country. When is something in this country, and why is this distinction made? The third is the dimension of scope. What is the pertinent art to which the invention pertains? How far into analogous fields can one look to find prior art? Interesting as all of these questions are, this article will focus primarily on the fourth dimension of prior art—that of content. This dimension delineates the types of sources that may be cited and used as references in determining nonobviousness. As an empirical matter, the most commonly cited references are prior patents and publications. It is clear, however, that other types of material are also in the prior art
