Concepts, for Deleuze, are . . . an ontological rather than an epistemological category. A concept is not . . . something that people have in their minds, but is rather a way of being . . . namely, the being of an intensive multiplicity.Levi Bryant (2008). Difference and Givenness: Deleuze’s Transcendental Empiricism and the Ontology of Immanence, 68
For Deleuze, the color red or redness is not a concept but a variation of white light. White light is a concept because it marks a difference in kind. Red or blue or any other color marks a difference in degree from other colors. White light is a necessary material or foundation for the production of all colors, and white noise is the foundation of all sounds. Colors are produced through the unmixing of white light. A prism demonstrates this process, as it spreads white light out into colors. Deleuze argues that concepts are generative.
“Deleuze . . . [argues] that there is no concept of the color red, but only of white light, of which red is a variation. If red does not form a proper Deleuzian concept, it is not because it is not real but because it does not mark the joints of being. Red marks a difference in degree from other colors, whereas color as such is a difference in kind. It is precisely in this sense that that Deleuze’s position evades the alternatives of realism and nominalism.”Levi Bryant (2008). Difference and Givenness: Deleuze’s Transcendental Empiricism and the Ontology of Immanence, p. 72
So, Deleuze is not claiming that the color red isn’t real (thus not a nominalist); it exists as a variation of white light. But he is also not saying that redness is a universal or a Platonic idea form (thus not a realist).
According to the Stanford Encyclopedia or Philosophy,
The word ‘Nominalism’, as used by contemporary philosophers in the Anglo-American tradition, is ambiguous. In one sense, its most traditional sense deriving from the Middle Ages, it implies the rejection of universals. In another, more modern but equally entrenched sense, it implies the rejection of abstract objects. To say that these are distinct senses of the word presupposes that universal and abstract object do not mean the same thing. And in fact they do not. For although different philosophers mean different things by universal, and likewise by abstract object, according to widespread usage a universal is something that can be instantiated by different entities and an abstract object is something that is neither spatial nor temporal. . . .
Thus one kind of Nominalism asserts that there are particular objects and that everything is particular, and the other asserts that there are concrete objects and that everything is concrete. . . .
Thus Nominalism, in both senses, is a kind of anti-realism. For one kind of Nominalism denies the existence, and therefore the reality, of universals and the other denies the existence, and therefore the reality, of abstract objects. But what does Nominalism claim with respect to the entities alleged by some to be universals or abstract objects, e.g. properties, numbers, propositions, possible worlds? Here there are two general options: (a) to deny the existence of the alleged entities in question, and (b) to accept the existence of these entities but to argue that they are particular or concrete.
Redness would be considered a universal or an abstract object (I don’t care which); it is a property that can be instantiated in various entities–red paint, red fire trucks, etc. For nominalists, redness exists only as a word signifying a property. Other abstract objects are the number five, tennis, freedom, and humanity. Universals are things like mammals, chairness, tableness, greenness, and goodness. Plato spoke of ideal forms, such as the ideal chair or ideal table, with all chairs and tables in sitting in homes being like shadows or images in a mirror, which come and go in time; so the ideal chair or table that is reflected in the mirror actually exists; it’s real. For Plato, we can have knowledge about ideal forms but only opinions about the copies.
For medieval Christianity, divinity is an essence, and the whole of creation is divided up according to degrees of divinity. God is, of course, pure divinity, and the angels possess a lesser degree of divinity; humans possess a lesser degree of divinity than angels, and so on. Below God, there are only differences of degree rather than kind. In this view, divinity is what it is without any admixture. It is a timeless essence. But for a Deleuzian, divinity could only be a mixture. It would be an intensive multiplicity.
Bergson argues that qualities like rationality, empathy, love, etc., are intensive multiplicities. As experienced by consciousness, they (intensities or affects) are all mixed up. They can’t be separated out and examined as if they occupied space, as if set out on a table to examine. They are experienced as duration, in time, and no particular intensity is precisely repeatable because the exact combinations of mixed up feelings cannot be repeated. Consciousness also changes.
Duration, according to the dictionary definition, is the time during which something continues. But duration is not simply time; it is not the difference between before and after, as stated by Luhmann, because one moment does not disappear as a new moment appears.
The relevance of Bergson to Luhmannian systems theory might be that social systems experience duration; they endure until they do not endure. In order to be a system, the system must endure from moment to moment; it must reproduce itself.