Emotion indicates a states of kind of arousal, a state that can prompt some activities and interfere with others. These states are associated with characteristics bodily expressions such as love, grief, anger, joy, fear. Unlike mood, they have objects: one grieves over some particular thing, or is angry at something.
It is convenient to speak of emotions having elements of various sorts (for example, thoughts, sensations, desires, feelings, pleasures, pains, shifts of attention) those should not be thought of as merely bundled together, and the emotion as a mere conglomeration. The truth is rather than an emotion is an ordered complex or structure of the element it is taken to comprehend, with causal relations prominent among those in which this order consists. My anger at my friend for not fulfilling promise he made, for example, is a bodily responses rooted in psychology and reflected in countenance, involving a focusing of attention on his/her and feelings of agitation and displeasure, which result jointly from my thought of his/her action and my desire that he/she should not have acted, while fuelling, perhaps, my desire that he/she is some way pay for having so acted.
It is not obvious that the states we call emotions have anything interesting or important in common that distinguishes them from all other mental states. Some have argued that what we call “the emotion” do not belong to a “natural kind” or class, and even that the concept of emotion should be banished entirely at least from scientific discourse.
Investigating bodily responses and feelings especially in the facial and skeletal muscles, which constitute the so called “expression” of emotions, one may contend that an emotion is the felt awareness of reverberations of the bodily reactions to something perceived or thought reactions such as trembling, quickening of pulse, crying, running or striking someone. It is this perception of one own bodily responses that endows each type of emotion, such as fear, anger, and joy with its special feeling quality. We may infer that the emotion states were effects rather than causes of these bodily reactions. The truth is that “we feel sorry because we cry, angry because we strike, afraid because we tremble, and not that we cry, or tremble, because we are sorry, angry, or fearful” so if the emotions are just a subclass of feeling qualities, and if these feeling qualities are caused by the bodily reactions that commonsense regards as manifestations or expressions of emotion, then common sense has it backwards.