- Basic emotions
- A proposed set of emotions that are universal, biologically based, and evolutionarily ancient. Ekman's canonical list includes happiness, sadness, fear, anger, disgust, and surprise. Criteria include a distinct universal expression, specific physiological signature, automatic appraisal, and brief duration.
- Plutchik's wheel of emotions
- Robert Plutchik's 1980 model proposes eight primary bipolar emotions (joy–sadness, trust–disgust, fear–anger, anticipation–surprise) arranged in a wheel by similarity. Emotions vary in intensity (petals closer to the centre are more intense) and adjacent emotions blend into secondary emotions.
- Universality hypothesis
- The proposal that certain facial expressions of emotion are recognised cross-culturally — even in pre-literate, isolated cultures with no exposure to Western media. Ekman's 1969 study with the Fore people of Papua New Guinea is the key supporting evidence; Barrett's 2019 meta-analysis is the key challenge.
- Categorical model
- Emotions exist as discrete natural kinds — fear is qualitatively different from sadness, not just lower on some dimension. Each category has a dedicated neural circuit (an "affect program" in Tomkins's term). Ekman, Izard, and Tomkins are the main proponents.
- Dimensional model (circumplex)
- James Russell's 1980 circumplex model proposes that all emotions can be located in a two-dimensional space defined by valence (pleasant–unpleasant) and arousal (high–low). There are no discrete categories — only regions of a continuous space. Core affect is the neurophysiological substrate.
- Affect programs
- Silvan Tomkins's term for the biologically fixed programmes that produce emotional responses. Each programme specifies a particular facial expression, autonomic nervous system change, and subjective feeling when triggered. Ekman adopted this concept to ground his basic emotions in biology.
- Action tendencies
- Nico Frijda's concept: each emotion prepares the organism for a specific type of action. Fear prepares for flight or freezing; anger prepares for approach and confrontation; sadness prepares for withdrawal and support-seeking. Action tendencies are the functional core of emotion.
- Emotion blends
- In Plutchik's model, adjacent primary emotions combine to form secondary emotions — joy + trust = love, fear + surprise = awe, anger + anticipation = aggression. Complex social emotions (contempt, guilt, pride) are understood as blends of more primary states.