Being so central to human experience, you might think psychologists have developed a consensus definition for emotions, but you would be wrong. There are, however, points of agreement. For example, emotions are not the same thing as feelings, but rather, feelings are just one component of emotions ― the subjectively experienced part. Alternatively, feelings can also just be physical sensations (such as feeling hungry or tired) apart from emotions, so not all feelings are part of an emotion, but all emotions feel some way. In addition to this experiential component, emotions have a physiological component (such as changes in heart rate or blood pressure). Such alterations in the autonomic nervous system prepare the body to respond to emotional stimuli, and also help shape feelings. A third component of emotions is the behavioral or expressive component (such as facial expressions or action tendencies). Action tendencies are urges to carry out behaviors that are characteristic of the emotions they accompany (such as running away in fear or fighting in anger). Emotions are also distinct from moods, which are like emotions, but are more diffuse and are experienced on a longer time scale (hours to months), and are different from personality traits, which can last a lifetime. Emotions, in short, are how we initially deal with situations that matter to us without having to consciously think about it.

     Emotions are mental states like thoughts, but they result from brain activity in response to interaction with emotionally-salient stimuli. Like thoughts, emotions are always about something, and are therefore intentional states (an unfortunate word that does not imply emotions are willed, but simply that they have a property of "aboutness"). If emotional stimululi are states of affairs that can be stated as propositions, then emotions are about propositions and can also be considered propositional attitudes (as are beliefs). Emotions result from cognitive appraisals of states of affairs that are emotionally stimulating. That is not to say that any conscious thought goes into forming emotions, but the brain does appraise the situation for features of emotional significance, and such appraisals help form appropriate emotional responses. So emotions are mental states distinct from states such as thoughts and beliefs, but they are influenced by these other mental states. Emotions are often contrasted with rational thought, but it seems rational thought would be very limited without emotions, because without emotions nothing can matter.