Past research on concepts has focused almost exclusively on noun-object con
cepts. This paper discusses recent research demonstrating that useful disti
nctions may be made among kinds of concepts, including both object and nono
bject concepts. We discuss three types of criteria, based on structure, pro
cess, and content, that may be used to distinguish among kinds of concepts.
The paper then reviews a number of possible candidates for kinds based on
the discussed criteria.