I hope I will be forgiven for abusing the term “skepticism” here — for what I have in mind is not a perfectly innocuous “claims require evidence” epistemic prudence, but rather Cartesian skepticism.
According to the Cartesian skeptic, one can be perfectly certain about one’s own mental contents and yet also be in total doubt about what really corresponds to those mental contents. Hence she needs an argument that will justify her belief that there is any external reality at all, and that at least some of her mental contents can correspond to it.
There are many responses to Cartesian skepticism, and here I want to pick up on one strand in the pragmatist tradition that, on my view, cuts deepest into what is wrong with Cartesian skepticism.
I think that one cannot talk, in any intelligible sense, about justification in the first place without also committing oneself to a belief in other minds with whom one shares a world. (Not that I like that way of putting it — “a belief in other minds” is a much too intellectualistic interpretation of the myriad ways in which we experience the sentience of nonhuman animals and the sentience-and-sapience of other human animals.)
I say this because justification is itself a social practice — and one that we ourselves are taught how to participate in. (In the contemporary jargon, I’m a social externalist about justification.) For what is justification? It is a normative assessment of the evidence and reasons for one’s claims. But that normative assessment necessarily involves other rational beings like ourselves.
Think of it this way (taking an example from Wittgenstein): suppose I’m waiting for a train, and I want to know if it will be on time. I could look up the schedule. But suppose further that instead of doing so, I imagine the schedule: I look up the time in my imagination. Why isn’t that the same thing as looking up the actual schedule?
The answer is that there’s no constraint on how I imagine the schedule. It could be whatever I want — or subconsciously desire — it to be. But without constraints, there are no norms or rules at all.
Justification is much the same: it is a normative assessment of evidence and reasoning according to rules or norms, and there are no private norms. (Though Wittgenstein doesn’t put it this way, he might say that the very idea of a “private norm” is a category mistake — a category mistake on which Cartesian skepticism and several hundred years of subsequent philosophy have depended.)
So whereas the Cartesian skeptic thinks that we need to justify our belief in the world and in other minds, I think that this makes no sense at all. We cannot justify our belief in other minds and in the world because there is no such thing as justification at all in the first place without also accepting (what is indeed a manifest reality to everyone who is not a schizophrenic or on a bad acid trip) that there are other sentient-and-sapient beings other than oneself with whom one shares a world.
.A further point to make (and the subject of my current article-in-progress) is that justification and truth require both sentience and sapience.
The clue I’m following is Davidson’s triangulation argument: suppose there are two creatures who are each responding sensorily to some object in a shared environment. How is an onlooker supposed to know which object they are both responding to? If both creatures can compare its own responses with the responses of the other creature, then each can determine whether or not they are cognizing the same object.
The point here is that two (or more) sentient creatures — intentional beings that can successfully navigate their environments — can each have a grasp of objectivity if and only if each creature can
(1) represent the similarities and differences between its own embodied perspective and an embodied perspective occupied by another creature and
(2) be motivated to minimize discrepancies and eliminate incompatibilities between its own action-guiding representations and its action-guiding representations of the other creature’s action-guiding representations, and in the process
(3) attain the metacognitive awareness whereby it can take its own embodied perspective as an embodied perspective, and thereby be aware that how it subjectively takes things to be is not (necessarily) how things really are.
This process is facilitated by a shared language that allows each creature to monitor how each is representing the other’s representations and revise its own representations when incompatibility between representations is discovered. The function of norms — of discourse and of conduct — is to motivate each creature to revise its representations when incompatibilities are discovered.
One important implication of this argument is that sentient creatures cannot distinguish between their own subjective orientation on things and how things really are. They lack an awareness of objectivity and an awareness of their own subjectivity. By contrast, sapient creatures are aware of both objectivity — how things really are, as distinct from how they are taken to be — and subjectivity — how things are taken to be, as distinct from how they really are.
This line of thought also explains why I have been adamant that objectivity does not require absoluteness: sapient creatures can be aware of the difference between how things are and how they are taken to be, and thus be aware that they might have false beliefs, even though no sapient creature can transcend the biological constraints of its form of sentience.