The organism befalls the body. The organism is the organized, the formalized body. But while the organism may “determine” the body at any given moment of its existence, it doesn’t define it. What then is a body?
As DG’s ontology is “flat,” their conception of the body is, in a manner of speaking, only two-dimensional. A body, say they, has a longitude and a latitude. It is defined (longitudinally or extensively) by relations and (latitudinally or intensively) by affects.
The relations that define a body longitudinally are relations between material elements moving at variable speeds. Relations are always relations of speed and slowness, movement and rest.
As Deleuze aficionado Manuel Delanda points out, the term affect is really shorthand for “capacity-to-affect” or “capacity-to-be-affected.” Delanda isn’t fond of the term because it is too easily mistaken for affection, i.e. emotion or passion. At best an emotion or passion is a component of an affect that subtends it. For example, I have an affection for my neighbor’s cat. This affection signals a capacity: a capacity-to-be-affected-by-this-particular-cat. But this “capacity” is not exhausted by the affection I feel for him. It also displays itself in other ways: like when he meows and I go to the fridge to fetch him the milk the order-word of his meow is demanding. A capacity thus manifests both in passivity and action: in the passivity of passion and the action of acts.
Reality is both actual and virtual. A capacity is real: but its reality is the reality of the virtual. Take my capacity to play the guitar a little. Even when I’m not playing, the capacity remains. You could submit me to an x-ray or MRI, but you’d be unable to locate this capacity. The virtual is real but nonlocalizable. Only actualities can be localized.
The reality of a capacity is variable. If I started practicing ten hours a day, my capacity to play the guitar would become greater: it would be more real, it would have more reality. If I stopped playing right now and never played again, the capacity would slowly start to dissipate, until it would resolve into a mere abstract possibility.
A body can thus gain affects and it can lose them. Perhaps the gain of one affect always involves the loss of others. Nietzsche said something to this effect in The Genealogy of Morals. As he points out, the loss of an affect is not always a bad thing. But it is also not always a good thing. Understood as the particular formalization of the body, an organism must always involve the canalization of affects or capacities. This holds true as much for the organism that befalls the junky as it does for the organism that befalls the smith.