[1] Plutchik proposed a psychoevolutionary classification approach for general emotional responses.

[2][3] He identified eight primary emotions—anger, fear, sadness, disgust, surprise, anticipation, trust, and joy.

Plutchik argues for the primacy of these emotions by showing each to be the trigger of behaviour with high survival value, such as the way fear inspires the fight-or-flight response.

Additionally, his circumplex model makes connections between the idea of an emotion circle and a color wheel.

[citation needed] Plutchik contributed the "Emotions" article to the encyclopedia, World Book Millennium 2000.