An emotion is a mental and physiological state associated with a wide variety of feelings, thoughts, and behaviours. It is a prime determinant of the sense of subjective well-being and appears to play a central role in many human activities. As a result of this generality, the subject has been explored in many, if not all of the human sciences and art forms. There is much controversy concerning how emotions are defined and classified.

Etymology and definitions

The English word 'emotion' is derived from the French émotion and émouvoir. This is based on the Latin emovere, where e- (variant of ex-) means 'out' and movere means 'move'. The related term "motivation" is also derived from movere.

Researchers distinguish feeling and emotion, where feeling refers to the subjective experience of the emotion. Some believe that emotions can occur unconsciously, and hence that emotion is a more general phenomenon than its subjective feeling. Feelings may also more narrowly refer to the experience of bodily changes. A second distinction focuses on the difference between the emotion and the cause of the emotion. For example do we say that thoughts about a loved one cause the emotion of love or that these thoughts are part of the emotion? One way to resolve this issue is to see whether the emotion can occur independently of these thoughts. Thus, thoughts about a particular person or situation could not be part of the emotion of love, since one can experience the same emotion about many other things.

Yet could one experience love without some thought or other of a loved person or object? If not, then we may stipulate that thoughts of a loved object are part of the emotion. Some theorists argue that at least some emotions can be caused without any thoughts or indeed 'cognitive activity' at all. They point to very immediate reactions (e.g. LeDoux 1996), as well as the conjectured emotions of infants and animals as justification here. Debate on this point is ongoing but represents a major distinction between what are called 'cognitive' theories of emotions and 'non-cognitive' theories of emotions, where non-cognitive theories regard some other feature of emotions, such as bodily responses to be essential.

A related distinction is between the emotion and the results of the emotion, principally behaviours and emotional expressions. People often behave in certain ways as a direct result of their emotional state, such as crying, fighting or fleeing. Yet again, if one can have the emotion without the corresponding behaviour then we may consider the behaviour not to be essential to the emotion. However some theorists such as Nico Frijda who hold a functionalist approach to emotions point to the idea that emotions have evolved for a particular function, such as to keep the subject safe. If the behaviours associated with an emotion are the determining factor for the very existence of that emotion then goal-directed behaviour should be regarded as essential to the emotion. Yet since we recognise that the behaviour need not necessarily occur, we can stipulate that emotions involve what are called 'action tendencies'. So for instance, fear involves the tendency to flee, which means that the probability that the subject will flee from a given situation is increased when he is undergoing fear.