Affect theorists tend to distinguish between affect and emotion. I will start with the latter, because it is easier to explain. Emotions are personal experiences or states, like anger, disgust, fear, happiness, sadness, and surprise: these are the six basic emotions catalogued by the psychologist Paul Ekman (2012), though we may well dispute his claims that this list is either exhaustive, or invariant across cultures. There are also more complex emotions, like humiliation, contempt, relief, jealousy, exhaustion, and so on; it is unclear whether these can be broken down into combinations of the more basic ones, or whether more specific cultural contexts need to be involved. It also isn’t easy to delineate the boundary between emotions and moods (which might include such conditions as melancholy, despair, and contentment). Presumably emotions are acute and momentary, while moods are longer-lasting and more stable, providing a general background to our more immediate experiences. But in spite of all these difficulties, we are generally able to recognize emotions in ourselves and others. Indeed, emotions are always attached to subjects or selves. They are conditions that come over us, or in which we find ourselves. They are states of mind that we experience directly. They tend to color and inflect—or even set the conditions for—nearly all of our other perceptions and actions.
Cognitivists and evolutionary psychiatrists understand emotions largely in functional terms. Emotions, they tell us, are shortcuts which aid us in making judgments necessary to our survival. If something tastes disgusting, I immediately spit it out; I might well die if I only rejected a given piece of food after having rationally determined that it was poisonous. But it seems to me that this sort of explanation is inadequate; it fails to account for the ways that emotions seem to take on a life of their own. They creep up upon us, overcome us, and sometimes overwhelm us. They can be dysfunctional and dangerous. Indeed, emotions can be (and often are) experienced—felt, enjoyed, or suffered—for their own sake, without serving any particular function, and entirely apart from anything that they might lead us to believe or do. Such vicarious experience is the basis of all aesthetics. Reading a novel, hearing a piece of music, or watching a movie is an emotional experience first of all. Cognition and judgment only come about later, if at all.
This situation is what leads affect theorists—following in the wake of such thinkers as Spinoza,(1992), William James (1981), Whitehead (1978), Deleuze and Guattari (1987), and Massumi (2002)—to differentiate between emotion and affect. If emotions are personal experiences, then affects are the forces (perhaps the flows of energy) that precede, produce, and inform such experiences. Affect is pre-personal and pre-subjective; it is social, or even ontological, before it is strictly individual. Affect isn’t what I feel, so much as it is what forces me to feel. Affect in this sense is not necessarily conscious; but conscious experience may well issue from it. Psychoanalysis tells us of drives that impel thought but cannot themselves be captured in thought; cognitive psychology tells us of computational processes that provide the basis for conscious awareness, but that cannot themselves be grasped within such awareness.
Affect theory accepts both of these formulations, but pushes them even further. It argues that drives and cognitive processes are themselves only instances, or specialized and limited aspects, of more general movements of affect. Affect is best understood—in Spinoza’s formulation—as any manner in which (using the word as a verb instead of a noun) entities in the world affect and are affected by one another. I see things in the light of the Sun’s visible spectrum, and I feel with pleasure the warmth of the Sun’s infrared rays on my skin. But I am also affected by the Sun’s ultraviolet rays; even though I cannot sense them directly, they may well impinge upon me in the long run, in the form of sunburn, or even of skin cancer. And as William James argued, I don’t feel a clenching in my stomach because I am afraid, so much as this clenching is already in itself my experience of fear. In this way, I already feel afraid, before I become aware of what it is that has frightened me. Our perceptions and our emotions are always drenched in affect, and driven by affect, even though affect per se is irreducible to perception or emotion.
This means that affect is at once both physical and mental; or better, affect precedes (and thereby escapes) the very distinction between the physical and the mental. Affect is also all at once both actual and vicarious. It is actual, because it happens within me as an alteration of my physical and psychological state. But it is also vicarious, because—as a process of alteration—it is independent of the things or forces that trigger it. I actually do feel fear, even when I am mistaken (that rustling in the grass was not actually caused by the movement of a poisonous snake), and indeed even in what I know to be fictional circumstances (as when I respond to the slasher in a horror movie). This is why affect is so central to our experience of audiovisual media artifacts (and indeed, of media and arts in general).
Steven Shaviro is the DeRoy Professor of English at Wayne State University. His books include Post-Cinematic Affect (2010), Melancholia, Or, The Romantic Anti-Sublime (2012), and Discognition (2016).
 Paul Ekman, Emotions Revealed: Understanding Faces and Feelings (New York: Owl Books, 2003).
 Baruch Spinoza, Ethics: with The Treatise on the Emendation of the Intellect and Selected Letters, trans. Samuel Shirley (Indianapolis: Hackett, 1992); William James, The Principles of Psychology (Cambridge: Harvard University Press, 1981); Alfred North Whitehead, Process and Reality (New York: The Free Press, 1978); Gilles Deleuze and Felix Guattari, A Thousand Plateaus, trans. Brian Massumi (Minneapolis, University of Minnesota Press, 1987); Brian Massumi, Parables for the Virtual (Durham: Duke University Press, 2002).
 Spinoza, 103.
 James, 1058-1097.