John Gray:

Socrates founded European thought on the faith that truth makes us free. He never doubted that knowledge and the good life go together. He passed on this faith to Plato, and so to Christianity. The result is modern humanism.
Socrates was able to believe that the examined life is best because he thought the true and the good were one and the same: there is a changeless reality beyond the visible world, and it is perfect. When humans live the unexamined life they run after illusions. They spend their lives searching for pleasure or fleeing pain, both of which are bound to pass away. True fulfillment lies in changeless things. An examined life is best because it leads us into eternity.
We need not doubt the reality of truth to reject this Socratic faith. Human knowledge is one thing, human well-being another. There is no predetermined harmony between the two. The examined life may not be worth living.
…The bequest of Socrates was to tether the pursuit of truth to a mystical idea of the good. Yet neither Socrates nor any other ancient thinker imagined that truth could make mankind free. They took for granted that truth would always remain the privilege of a few; there was no hope for the species. By contrast, among contemporary humanists, the Greek faith that truth makes us free has been fused with one of Christianity’s most dubious legacies — the belief that the hope of freedom belongs to everyone.
In any case, only someone miraculously innocent of history could believe that competition among ideas could result in the triumph of the truth. Certainly ideas compete with one another, but the winners are normally those with power and human folly on their side…Evolutionary psychologists have shown that deceit is pervasive in animal communication. Among humans the best deceivers are those who deceive themselves…In a competition for mates, a well-developed capacity for self-deception is an advantage. The same is true in politics, and many other contexts.
But life does not work that way. Its very strength, is robustness, depends on not being a stickler for always insisting on the truth. Descartes himself acknowledged that while he was in the process of demolishing, razing to the ground, all the false ideas he had accumulated over a lifetime, he was obliged for the time being to “carry on my life as happily as I could”… To this end, Descartes decided to do what his philosophy tells us not to do, namely, follow if necessary “opinions most dubious” as if they were rock-bottom truths, and treat the merely probable as if it were certain.
If striving after truth ruins your well-being and makes you mope, if it shuts out the rest of the world and warps your temperament, what sense is there in making such a Herculean effort, especially if, at the end of it all, truth slips out of your grasp? In writing about the pursuit of philosophy, Hume repeatedly uses such terms as “fatigue”, “painful”, “burdensome”, “melancholy”. It is as if philosophy were some excruciating chore that makes the joints ache and the head throb, a two-Excedrin occupation.
…The human constitution, our biology and psychology, “Human Nature”, militates against a hermetic, solitary dedication to the truth, at least in most people, Hume suggests. In his own case, it tended to estrange him from the rest of the human species, leaving him “affrighted and confounded.”
…Our belief that we know the ultimate principles standing behind aspects of the world’s behavior is one of the mind’s illusions. The question is, how far should we surrender to those illusions? For Hume, that is a queasy predicament. To go along with all of them might make him the laughingstock of the intellectual community. At the other extreme is reason acting alone, and reason tends to feed on itself and lay waste not only philosophy but ordinary life as well. Hume is in a fix and he knows it. Should he continue to torture his brain with “subtleties and sophistries”, knowing that reason cannot justify human beliefs or prove them true? Or should he indolently subscribe to the “general maxims of the world” —an echo of Montaigne — throw his books on the fire, order a high-cholesterol dinner, and have a hilarious evening with his chums?
I have no problem with accepting that there is no such thing as “ultimate” truth, because like all human concepts, truth is defined only in relation to its opposite. Truth is not reality, it’s a idea about reality. It seems like we especially have trouble accepting this when it comes to concepts of morality. If I say that it makes no sense to talk about a state of affairs in which “everything is up”, that seems obvious — what does it even mean to talk about something being “up” without an understanding of “down”, or the potential for it to exist? But suggest that there can be no truth without falsehood being the other side of the coin, or that “good and evil” are twins as well, and people tend to act as if you’ve just set fire to the very fabric of the universe.
But I still find it useful to use a concept of truth as a polestar, as something to orient oneself around, without believing that it can ever be possessed purely and totally. Conditional truth is good enough. The alternative, to me, is accepting some form of mythological thinking, in which we base our lives on feelings rather than abstract concepts. I was thinking about that recently as I tried once again to carry on a conversation with my right-wing relatives. In one instance after another, there is simply no common ground upon which to enter into mutual understanding, because we just aren’t speaking the same language. Or, rather, we’re using the same language toward different ends. For me, it very much matters whether a particular source is reliable, or whether a given claim is true. For them, what matters is that an anecdote, a “fact”, or a belief reinforces a mythical worldview, one in which the theme is more important than the details. If forced to relinquish a particular claim, they’ll just replace it with another one. At no time is the underlying worldview called into question. That’s the ground, the base, the starting point. Everything else follows from that. And while some false beliefs are more or less harmless, what are you going to use as a basis for saying that the harmful ones should be avoided or challenged?