The historically contingent identity of 'wholes' is defined by their emergent properties, capacities, and tendencies. What we need is a concept that allows us to retain both irreducibility and decomposability, a concept that makes the explanation of synthesis and the possibility of analysis intelligible. We will refer to these wholes as assemblages.

The identity of an assemblage is always contingent and it is not guaranteed by the existence of a necessary set of properties constituting an unchanging essence. Or to put this differently, assemblages are not particular members of a general category but unique and singular individuals. Even if two assemblages resemble each other so much that no one can tell them apart, each will still be unique due to the different details of its individual history. All these different assemblages are born at a particular time, live a life, and then die. It follows that knowledge about an assemblage does not derive from a "botanical" classification that takes properties for granted but from an account of the origin and endurance of those properties.

Given the importance of the ontological status of assemblages we will need a technical term to refer to it: every actual assemblage is an individual singularity. Emergent wholes are defined not only by their properties but also by their tendencies and capacities.

Although each assemblage is a unique historical entity it often belongs to a population of more or less similar assemblages. In other words, despite the individual singularity of each assemblage the process of assembly behind it tends to be recurrent so what is synthesized is never a single individual but many of them. To facilitate "population thinking" we need a means to specify not only the possible ways in which the members of a population can change but also the state of their identity at any particular point in their history. This can be achieved by parametrizing the concept of assemblage, that is, by providing it with modifiable settings: the values which determine the condition of the identity of an emergent whole at any given time.

The more homogeneous the internal composition of an assemblage and the better defined its outer boundaries the more "territorialized" its identity may be said to be. The identity of an assemblage is not only embodied in its materiality but also expressed by it. This distinction corresponds to that between matter-energy on one hand and information on the other, not the semantic information conveyed by the meaning of words or sentences, but raw physical pattern.

While the distinction between the material and the expressive, between matter-energy and information, is important to track the parallel histories of bodies and minds, it is also relevant because computer simulations are emergent wholes composed of information existing above the computer hardware that provides their material and energetic substratum. The technology that makes simulations possible had to undergo several transformations that can also be explained within the framework of assemblage theory. Thus the first deterritorialization brings the metalevel (operations on data) into direct contact with the object level (data) creating the possibility of assemblages made out of operators and data. The main danger of this account is making universal singularities into transcendent entities, entities existing entirely independently of the material world. It will point to an intimate link between ontology and epistemology. And the existence of such a link, in turn, will constitute a powerful argument for breaking with the ontology we inherited from the classical Greek philosophers, an ontology based on the general and the particular, and an incentive to develop a new one based on the individual singular and the universal singular.