I present a computational level account of how people combine concepts
, and I use this account to evaluate current models of conceptual comb
ination. Constrained by this account, I then provide an algorithmic le
vel description of how people combine concepts. The algorithmic level
account highlights the importance of two additional processes (compari
son and construction) in explaining how some concepts combine and chan
ge. 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 n
ot both.