Life and Other Vague Categories

Awhile back I proposed that the distinction between what is cognitive and what is non-cognitive is problematic because of the types of categories we're dealing with - namely, vague artefact categories rather than clearly bounded natural kinds. I suggested that this causes important problems for the study of cognition itself (because we have no principled method for deciding what counts as cognitive) and for philosophical arguments related to cognition (e.g., the coupling-constitution fallacy) because these also depend on having some idea of what counts as cognitive.

So, I went to a Cafe Scientifique talk recently by a Dr. Terry Kee, a chemist at the University of Leeds who studies the origins of life. He was a great speaker and he got the audience going by having us think through possible definitions of life. People trotted out the usual contenders like "can reproduce" or "has volition". Of course, there are always troubling counter-examples to simple criteria like this. The late biochemist Daniel Koshland gave a good example of this type of problem in a brief paper he wrote for Science:

“...'The ability to reproduce—that is the essential characteristic of life,' said one statesman of science. Everyone nodded in agreement that the essential of a life was the ability to reproduce, until one small voice was heard. 'Then one rabbit is dead. Two rabbits— a male and female— are alive but either one alone is dead.' At that point, we all became convinced that although everyone knows what life is there is no simple definition of life" (Koshland, 2002 p. 2215).

I had learned about this problem in high school and university biology courses, but I hadn't thought about it recently. Here was a similar problem in biology and chemistry as the one psychologists have with cognition. Unlike the cognition problem, however, there are some pretty good definitions of life available (e.g., Koshland, 2002). But these definitions aren't perfect. For one thing, there is the prickly problem of where to put viruses - they don't meet all the requirements for life, but they are certainly not NOT alive either. This is an especially interesting problem because it turns out that a lot of our DNA, regions of "junk" DNA, are actually remnants of ancient retroviruses. Then, there's the problem of all the intermediate forms that led to full fledged life - when did the switch flip from "here are a bunch of chemicals" to "here's a living thing"? For that matter, what status do we give to all the sub-components of life? Complex molecules like amino acids are necessary participants in living systems, but they are not, themselves, alive. So, it's not just that definitions of life are imperfect, it's that life is the kind of thing that cannot, by virtue of its category structure, be precisely defined.

Yep, life is a vague category. In my previous post I argued that definitions of graded categories can't  be resolved by acquiring more information. Definitions of life will always be unsatisfactory just like definitions of cognition will always be unsatisfactory. Some things really are kind of alive and kind of not alive, some systems really are kind of cognitive and kind of not cognitive. I suspect that the similarity between the category of living things and the category of cognitive things has to do with the fact that both life and cognition (whatever definition you use) are emergent properties. The building blocks of life are not alive and the building blocks of cognition are not smart. But, I need to chew on this idea for a while before I write more about it.

This is not to say that we can't study living things or psychological phenomenon like memory and decision-making. But, we do need to be up front about the inherent ambiguity in some of the terms we throw around. What in the world does it mean to say that memory is a cognitive process?

Some people use this term to suggest that memory is not an affective process. Some use it to mean that it is not a perceptual process. Some simply mean that it is a process that somehow has something to do with the brain. I personally don't think there is anything to be learned about memory (or decision-making or categorisation, etc.) by calling it a cognitive process. And I say this as a cognitive psychologist.

In future posts I'm going to address head-on the issue of what we get (and what we lose) by using the term cognitive. I'm also going to propose an alternative way to address the problem that focuses on defining cognition in terms of a thing's effect on an environment rather than in terms of the properties of the thing, itself.

But I just wanted to take a moment to notice that we psychologists are not alone in having a problematic category at the heart of our science and that's a comfort.


Koshland, D E (2002). The seven pillars of life. Science, 295, 2215-2216.