Dogmatism and relativism, obscurantism and doubt fall short because they are incapable of acting on reasonable supposition; like a computer unable to read a programme in which one digit has been typed incorrectly they cannot infer the relative likelihood of alternatives, which in human affairs can result in both tyranny and a kind of proud apathy which invites the tyranny of others.
Logic does not always seem to go hand in hand with reason. From Descartes, from Berkeley, from Kant, Locke and Hume, come propositions that may seem superficially to push us further away from enlightenment rather than towards it.
It takes Darwin to bring us back to earth: survival cannot be effected via random and misleading sense impressions.
It is a fact that because our perception of reality and the world outside of our heads must be mediated by our own sensory equipment, and is thus entirely dependant upon them, we could never perceive reality as anything other than our own sense-impressions, opening the door to the possibility that it is entirely different from our perception of it or even illusory.
Likewise, it is a fact that no object can truly be said to have a colour, or a smell or a taste, since these properties are determined by us as agents of perception, and are meaningless without us. Yet an apple can still exist in a world without us, so whatever it truly is, independent of the means to perceive it in other things, it cannot logically be said to be smooth, or sour, or green. But in that case what is it? How do we define anything other than by properties such as shape, texture or colour?
Such observations are invaluable as starting points to logical analysis, clearing the decks of unwarranted assumptions and inaccurate first principles.
But to pretend they represent non-negotiable barriers to progression - as Hume or Berkeley or Descartes would never have claimed - and therefore represent the end of the argument is absurd - and unscientific.
Russell called common sense "the metaphysics of savages". It is nothing of the sort. It is a tried and tested evolved mechanism that enables us to negotiate and survive in a world in which all living things evolve in concert. So when Richard Rorty says things like “truth is what your contemporaries let you get away with” or “no period of history gets reality more right than any other” he is saying something that is true, misleading, obvious and meaningless all at once.
He posits an alternative to Kantian idealism that in its particulars sounds a lot like it, only without the basic assumption that reality can withstand such unreasonable extensions of logical argument.
In going so far as to question whether the mind is even attempting to hold a mirror to reality Rorty elevated the reductio ad absurdum to the status of fundamental truth.
More than a mere spiv like Derrida, he was nonetheless too in thrall to the same kind of impish nihilism that animates deconstruction, the refusal to see that informed supposition is not wild guesswork but probably the greatest advance in the history of mental life on earth, the single most significant factor separating human minds from those of every other living thing. Hume in fact talks of 'mitigated scepticism', essentially an informed compromise between what little we know with certainty and what we may reasonably assume, negotiated for the express purpose of getting through life sensibly and safely.
So while no meaning or meanings can ever be prioritised in logic, some can be, must be, in practice if we are to function as natural entities, and claiming otherwise is just an intellectual game; fundamentally unserious, and trivial.
Existence is enacted not in an abstract world but a concrete one, with perils and challenges around every corner of a sort through which relativism is simply incapable of negotiating a course. This world is shaped by and subservient to natural laws to which we, as products of Darwinian evolution, can be predicted to respond in finite ways. In other words, ultimate truth may be forever elusive, but compromise is not merely possible but imperative. Some courses of action work, others do not. We accept this without question in our physical lives - why should our mental lives be so different?
Can we ever be sure how I see, feel or otherwise experience a tree, or liquid, or the colour green is the same way that you experience those entities we both call a tree, or liquid, or the colour green?
In logic, no we can’t, but in practice, it is not evasion to conclude, cautiously, that we can. If there was ever a person who saw a hungry tiger as the colour green he would not be expected to produce many ancestors. So in a sense, our existence suggests the question was answered long before it was even asked: radical doubt tested in the arena of empirical reality, with empirical reality (represented by the one with the stripes, long teeth and full belly) emerging the winner.
We are the descendants of a long line of reproducing entities that stretches back through human history all the way to the first self-replicating single-celled organism. Not one of our ancestors died before producing another generation. It is reasonable to suppose then, that our version of reality is, if ultimately just that, still nonetheless consistent with the reality perceived by all other successful perceiving entitles on the planet: and what better definition of objective reality than that are you looking for exactly?
Rorty wrote that “no organism, human or non-human, is ever more or less in touch with reality than any other organism” as if he was saying something interesting, but to be equally in touch with reality is exactly what we should expect of successful organisms.
Reality can be discerned in the areas of consensus and interaction between discrete entities, be they species, cultures, individuals or whatever.
This consensus points to exactly that objectively verifiable reality which the Cartesian method, transcendental idealism and postmodernism all question (the first two soberly and wisely). That we are not able to reach ultimate certainty on such questions merely says something about the limitations of our minds, nothing at all about phenomenal reality. You may as well argue from the perspective of a pencil and say there is no good reason for believing in the existence of cows, because a pencil cannot perceive them.
Rorty knew this: he wrote that beliefs are merely ingrained habits, road tested in the Darwinian arena, but didn't seem to grasp that this points towards an independently discernible reality rather than away from one.