How emotions should be classified? Are emotions distinctive states or do they vary smoothly along underlying dimensions?

James Russell (1979) model is an example of the latter, placing emotions along bi-polar dimensions of valence and arousal. Ekman divides emotions into basic and complex categories where emotions are considered foundational to the existence of others. Complex emotions may be regarded as developments upon basic emotions.

Such development occurs due to cultural conditioning. Alternatively, primary emotions could blend together to form the full spectrum of human emotional experience. For instance interpersonal anger and disgust could blend to form contempt in the model of Robert Plutchik.

Other theories argued for the existence of meta emotions which are emotions about emotions. Discussion centres around which emotions should be considered foundational. Combined views are also available.