When concepts combine.

I present a computational level account of how people combine concepts, and I use this account to evaluate current models of conceptual combination. Constrained by this account, I then provide an algorithmic level description of how people combine concepts. The algorithmic level account highlights the importance of two additional processes (comparison and construction) in explaining how some concepts combine and change. I then show that the interpretation of nominal metaphors involves these processes as well. Current approaches to metaphor understanding emphasize the importance of one or the other of these processes, but not both.