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Among discrete emotions, basic emotions are the most elemental; most distinct; most continuous across species, time, and place; and most intimately related to survival-critical functions. For an emotion to be afforded basic emotion status it must meet criteria of: (a) distinctness (primarily in behavioral and physiological characteristics), (b) hard-wiredness (circuitry built into the nervous system), and (c) functionality (provides a generalized solution to a particular survival-relevant challenge or opportunity). A set of six emotions that most clearly meet these criteria (enjoyment, anger, disgust, fear, surprise, sadness) and three additional emotions (relief/contentment, interest, love) for which the evidence is not yet quite as strong is described. Empirical approaches that are most and least useful for establishing basic-emotion status are discussed. Basic emotions are thought to have a central organizing mechanism and to have the capacity to influence behavior, thoughts, and other fundamental processes.
Robert W. Levenson (Tue,) studied this question.