I am an anti-essentialist in many respects, though there are some ideas denoted by some senses of the term to which I would not give assent. For example, I believe in a primitive kind of individual essence that explains the persistence of identity through change. However, I certainly do not believe in robust generic essences of the Aristotelian kind that incorporate a telos, ideal potential or proper function as an intrinsic property of the thing itself. The first reason is that such a view presupposes an objective form or natural kind to which each thing belongs, and I reject that more basic view, at least in relation to biological kinds and probably in relation to all things.
However, I just wanted to clarify that I do believe in a more direct problem for the idea of intrinsic proper function. It is that the supposed telos of a thing is usually much narrower than its range of dispositional properties that can causally interact with an environment and achieve an outcome that could be regarded as a good. For example, a common example of telos is that the acorn carries within it the potential to flourish as it interacts with fertile soil, water, air and sunlight to produce an oak tree. However, most acorns never do grow into acorns. Instead, they feed herbivores foraging over the forest floor. Most acorns serve the good of sustaining these other creatures, who have a claim on life at least equal to that of the oak tree. Why, then, is the telos of the acorn not regarded as reaching its fulfilment in the nourishment of small, forest-dwelling mammals?
I would suggest that this is not a peculiar example, but that the good-producing dispositional properties of things are always insufficiently determinate to objectively individuate an intrinsic telos. Hence, our intuitions of proper function are either mere impositions upon a world otherwise undifferentiated in that way, or those intuitions are made true by an external normative demand placed upon things of the given kind, much like a moral demand is imposed externally, but objectively, by divine command, in my view. I obviously prefer this final option. Note that this argument does not concern an epistemic deficit. It is based on the metaphysical principle of there being no distinction without a difference, which may not be true of things, but is most probably true of properties. That includes both determinable properties (such as that of ‘being coloured’) and determinate properties (such as that of ‘being coloured red’), which I mention because ‘being disposed to produce some good’ is of the former category and not the latter. To defeat the objection, we would need some substantive (non-question-begging) difference between the telos of a thing and other good-producing dispositions of that thing.
To finish, I have another clear counterexample to intrinsic proper function, which is the case of the spermatozoon (singular form of ‘spermatozoa’). The proper function of the spermatozoon is to fertilise the female ovum, and yet it is of the good that only one spermatozoon (in the overwhelming majority of cases) will have this honour. Most can be said to have achieved a good end by getting close to this objective and available for it, but not achieving it. Otherwise, a grotesque cellular monstrosity would be abortively conceived. Statistically, far more of them achieve this good than that of fertilisation. Once again, their good-producing dispositional properties are insufficient to determine what our intuitions might invite us to see as their proper function, i.e. fertilisation.
To this it might be responded that it is the dispositional properties of the ovum that result in the redundancy of all but one spermatozoon, and not of the spermatozoon itself. However, this would be to misunderstand the nature of dispositional properties, which always relate to dispositional pairings, such as that of sugar and water. The disposition of sugar to dissolve in water does not make sense without the obverse dispositional property of water to dissolve sugar. Their dispositions cannot be understood in isolation. Similarly, the good-producing disposition of the ovum to reject all spermatozoa pipped at the post is matched by a good-producing disposition of all such spermatozoa to be rejected. So, why is the proper function of a spermatozoon not to get really close but fail at fertilising an ovum?
Another response might be to make the telos of the spermatozoon disjunctive. That is, its proper function is to either fertilise the ovum or get close enough to have been available after another gets there first. Yet, we can then put pressure on the notion of being available to fertilise, without doing so, for its vagueness. How close to fertilisation does it need to get for it to be available? Note that there is no predetermined correlation between any given spermatozoon and ovum pairing beyond that of reproductive compatibility within the same species. Furthermore, without getting into details, there is a vast range of locales in which a spermatozoon could come to rest and yet still be applied thereafter to the successful fertilisation of a compatible ovum somewhere in the world. Given this potential, and given that there are many ova of the same species in the world at any given time that have already been fertilised, just recently, by another spermatozoon, is there ever a spermatozoon that has not achieved this disjunctive telos? And yet, our intuitions tell us that such achievements are contingent and rare. This becomes an argument ad absurdum against the very idea of intrinsic proper function.
Overall, that is the underdetermination objection.
Theocentric Posthumanism 