Traditional theories of categorization in which categories are assumed to b
e grounded in perceptual similarity or theories ignore an important basis o
f conceptual structure: the emotion that a stimulus elicits in a perceiver.
This article discusses the nature of, constraints on, and conditions of us
e of emotional response categories. Experiments in which participants sorte
d triads of concepts that shared both emotional and nonemotional relations
indicate that individuals use emotional response categories when they are e
xperiencing emotional states. Multidimensional scaling of similarity judgme
nts by emotional and nonemotional perceivers supports a selective attention
mechanism of these effects. Participants induced to feel happy or sad emot
ional states weighted the emotional responses associated with stimuli more
heavily than people in relatively neutral states. The triad and multidimens
ional scaling findings, along with functional considerations, suggest that
emotional response categorization is not only tenable, but necessary for a
complete account of categorization.