Notions of individuality

What does it mean to call something “an individual”? When is it appropriate to do so, and why? In particular, according to what criteria do we draw the boundaries of individuality between the agent and its environment?

Let me be more clear about what I do and don’t have in mind when I talk about individuality here. Specifically, I am not interested in individuality in the sense of personal identity or inquiries about “the Self”. Instead, I am specifically interested in answering how to draw boundaries around agents.

This may in part or entirely be a matter of epistemology and philosophy of science in that we are attempting to provide more conceptual clarity, or at least clearly point at an existing conceptual confusion, with respect to the explanatory role notions of inviability play in our scientific attempts of making sense of the world. However, it may also be the case that this is not “merely” a question of modelling conventions. In adopting, at least temporarily, an assumption of “realism about individuality”, we may ask ourselves whether there are substantive things to be understood about what makes something an individual. (In my own inquiries, I am certainly trying to take the realism hypothesis seriously.)

Many theories across virtually any scientific discipline rely, implicitly or explicitly, on some notions of individuality. However, it is my impression that individuality is largely under-theorized. This can lead to inconsistencies when trying to explain phenomena in a way that builds on (unconvincing or inconsistent) notions of individuality.

For example, if we don’t really know what we mean by “an individual”, we risk using slightly different interpretations at different places within the same theory. It may then appears as if inexplicable discrepancies or “paradoxes” emerge but in fact, the paradox would not be a paradox if we realized we were substituting the same term (“an individual”) for different things. Or, inversely, in inadvertently using different notions of the individual, we may patch over discrepancies in our theory that really are there and that we really should notice, but the patch can make it look like the theory is coherent or unproblematic. A different problem can arise when the concept of an “individual” is used differently in different theories, making them incommensurable. In the name of scientific progress and the ambition to reach an ever more comprehensive understanding of how the world works, we are interested in having theories from different fields be able to “talk to each other” and - eventually - be reconciled. Inconsistent usage of such fundamental concepts as individuality will hamper this undertaking.

Lastly, and this is something I have already noted elsewhere, as a philosopher I feel a special responsibility to contribute to the endeavour of conceptual deconfusion. If empiricism is the bread and butter of science, conceptual deconfusion is the kitchen utensils and the cutlery we need to make bread and spread butter. The idea of individuality - the idea that there is a correct answer to the question of how to draw a line between an agent and its environment - is so fundamental to virtually any theorizing that it affects our understanding of a lot of other concepts of key interest. How can we understand agency (or any notion of goals or goal-directed behaviour, for that matter) if we aren’t able to point at an agent? What is causality if not based on some fundamental distinction between things (that can cause each other)? How should we understand notions of rationality if we cannot coherently point at agents that are supposedly acting rational (or irrational) in the context of a given environment? What is it that the concept of freedom tries to refer to if not something to do with the relationship of an individual to its Umwelt? Any notion to do with coordination (be it altruism/egoism, competition, or symbiosis) is premised on there being several entities that can coordinate with each other.  

The list goes on. Looking at this list, it bugs me to think that we might not even know whether the “individual” that we are looking to identify and delineate in each of these cases (causality, agency, rationality, freedom, coordination, etc.) points at one and the same phenomena (c.f. realism about individuality), or whether it is merely a matter of linguistic conventions and path dependency that we are lead to assume they do. (To put it differently, we may wonder whether the term “individual” or “individuality” is just an umbrella term that refers to many superficially similar-looking but fundamentally different things (or phenomena or processes), or to one-and-the-same underlying and fundamental thing (or phenomenon or process).)

It is in this sense that I want to understand the notion (or notions) of individuality better. I am sympathetic to the hypothesis I formerly dubbed “realism about individuality” - the idea that there is a natural category that is individuality, governed by the same principles across different modalities of implementation/manifestation. That said, I also believe that different fields, despite using at times very different notions of individuality (or, at least, different ways to talk about and formalize it) likely have interesting insights to contribute to the question of individuality - not in small part thanks to a certain theoretical pragmatism (e.g. choosing notions of individuality that lend themselves to talking about the things they want to talk about). 

So, what do different fields' answers to the question of individuality look like? For substantial answers to this question, the reader will have to wait for future posts in which I will be doing deep dives on specific fields and theories. However, there are a few observations that I want to share here already. 

First, it is in fact not as straightforward as it might seem to identify whether a theory in question is about individuality in the sense we are interested in here (precisely because we don’t (yet?) quite know what individuality is). To the extent that we assume that physics, biology and the social sciences (for example) all have things to say about how to draw boundaries around agents (without needing to assume anything about whatever their respective propositions are of equal epistemic merit), it is in fact not surprising that the type of answers these fields provide often look extremely different. The challenge then consists in figuring out whether, in fact, those theories talk about different things or phenomena, or whether it is a legitimate and valuable enterprise to try to figure out how to render those different theories commensurable (based on the assumption that they are in fact pointing in essence at the same sort of thing). As a result, someone undertaking this endeavour should expect to look into a theory and sometimes learn something new and substantial about the nature of individuality, and sometimes learn that what they have learned about was (maybe interesting but) not about individuality (in the sense they are interested in it) at all.  

Second, when doing a high-level scan of how different fields theorize individuality, it quickly becomes apartment that they are different types of explanations that can be given. One distinction that I specifically want to point out at this point is between top-down, descriptive and bottom-up, generative explanations. For example, biology typically relies on notions of individuality which are based on a list of observable properties. For example, an individual is defined as that which constitutes a unity of reproduction, or a unit of metabolic activity, or a unit delineated by a cell membrane (or similar physical signature), etc. While this way of defining individuality can appear locally sufficient, it comes with certain epistemic drawbacks and inadequacies. In the case of biology, for example, it doesn’t take long for those top-down, descriptive notions of individuality to run into trouble, e.g. when they fail to give useful answers to how to draw agent boundaries in the context of uni- vs multi-cellularity, “superorganisms” like ant colonies, mechanisms of genetic transfer beyond chromosomal transfer, etc. 

We might think that instead of such top-down definitions of individuality, what we rather want is a bottom-up, generative framework for identifying the agent-environment boundaries (e.g. Krakauer et al., 2014, “Information Theory of Individuality“ or Levin, 2019, “The Computational Boundary of a “Self””). To the best of my knowledge, attempts of this type are as of yet relative rare and underdeveloped - but they sure seem worth keeping an eye on. 

Third, so far, I have talked a lot about the idea of looking at how different fields approach the questions of individuality and agent boundaries. This asks for an important methodological point of clarification. I am not (primarily) interested in different fields’ perspectives on this issue for reasons related to the history and sociology of science. More importantly, I am using scientific fields as a proxy for assemblages of knowledge about different types of natural systems. For example, the field of biology is delineated (largely) by the fact that its objects of study are biological systems. Respectively, the social sciences study social systems, etc. Related to the notion of “realism about individuality”, the endeavour I am pursuing here is about figuring out whether individuality is expressed by principles, processes or mechanisms that are essentially the same across their modality of implementation (i.e. whether they are implemented in a biological, social or physical system). Now, this is not a completely innocent idea. For example, someone might point out that any sociological system is essentially implemented on top of a biological system, and that any biological system is essentially implemented on a physical system. That certainly seems right to me. However, we might still think that, from an epistemological and certainly sociology of science point of view, different levels of explanations and different epistemic communities will be better placed to talk about certain systems more so than others. Therefore, the abstraction into social, biological, physical etc. systems may well be justified and useful.