Etymologically, the word emotion is a composite formed from two Latin words. ex/out,outward + motio/movement,action,gesture. This classical formation refers to the immediate nature of emotion as experienced by all, indeed living organisms.

In psychology and common use, emotion is an aspect of a person's mental state of being, normally based in or tied to the person's internal (physical) and external (social) sensory feeling. Love, hate, courage, fear, joy, sadness, pleasure and disgust can all be described in both psychological and physiological terms. Emotion is the realm where thought and physiology are inextricably entwined, and where the 'self' is inseparable from our individual perceptions of value and judgement toward ourselves and others.

Emotion is sometimes regarded as the antithesis of reason; as is suggested by phrases such as appeal to emotion or don't let your emotions take over. It must be recognized that emotional reactions often produce internal states and cognitive streams undesirable to the individual feeling them, which s/he may wish to control but often cannot, or at least produce consequences or thoughts which s/he may later regret or disagree with but during the emotional state, could not control with his/her other principles. Thus one of the most distinctive and perhaps challenging facts about human beings is this potential for both opposition and entanglement between will, emotion, and reason.

Some state that there is no empirical support for any generalization suggesting the antithesis between reason and emotion: indeed, anger or fear can often be thought of as a systematic response to observed facts. What should be noted, however, is that the human psyche possesses many possible reactions and perspectives in response to the internal and external world - often lying on a continuum— at one extreme lies pure intellectual logic (often called "cold"); at the other extreme is being purely emotionally unresponsive to logical argument ("the heat of passion"). In any case, it should be clear that the relation between logic and argument on the one hand and emotion on the other, is one which merits careful study. It has been noted by many that passion, emotion, or feeling can add backing to an argument, even one based primarily on reason - particularly regarding religion or ideology, areas of human thought which frequently demand an all-or-nothing rejection or acceptance, that is, the adoption of a comprehensive worldview partly backed by empirical argument and partly by feeling and passion. Moreover, it has been suggested by several researchers that typically there is no "pure" decision or thought, that is, no thought based "purely" on intellectual logic or "purely" on emotion - most decisions and cognitions are founded on a mixture of both.

Culture, society and emotion

It is not clear whether emotion is a purely human phenomenon, since animals seem to exhibit conditions which resemble emotional responses such as anger, fear or sadness.

It has been hypothesized that the emotional responses typical of human beings have evolved and changed in many ways since the species first emerged. Nonetheless, as noted above, it may well be the case that human and non-human animal emotional responses lie on a continuum, rather than being two completely distinct categories of human and animal.

Much of what is said about emotions, as well as the history of what has been said about them, is conditioned by culture and even politics. That is to say specific emotional responses, as well as a group's interpretation of their significance, may be influenced by cultural norms of propriety. For instance, certain emotions such as love, hate, and the desire for vengeance are treated very differently in differing societies. This methodological relativity is entirely different from the question of whether emotions are universal or are culturally determined. Many researchers would agree that a vast proportion of human behavior, no matter how close to the lowest biological substrates - including sexual behavior, food consumption, feelings in response to physiological changes and responses to environmental conditions - are conditioned based on social surroundings and non-human environmental factors. Thus it is not difficult to defend the position that emotion is, to a high degree, dependent on social phenomena, expectations, norms, and conditioned behavior of the group in which an individual lives. Clearly, then, the influence of politics, religion, and socio-cultural customs can be easily traced or hypothesized, or perhaps not. Among many pertinent examples: behaviors or activities considered highly cruel in some societies may in fact provoke responses of enjoyment in others; or, sexual acts considered highly desirable in some cultures would provoke shame or disgust in others.