The psychological aspect that seems to be the best single discriminator between left and right appears to be their relative locations on the scale of epistemic confidence.
Left and right seem to be, more than anything else, evolved psychological dispositions from which moral foundations, moral matrices, and the values, principles, and ideologies associated with them, follow. They’re cognitive operating systems that process more or less the same inputs only to arrive at dramatically different outputs. To think of them primarily in terms of the outputs – the value systems or ideologies they espouse in any particular time and place – is to put the cart before the horse.
Those two operating systems are described in the book The Cave and the Light: Plato Versus Aristotle, and the Struggle for the Soul of Western Civilization, by Arthur Herman. Plato and Aristotle serve as metaphors that sum up the two operating systems.
To the left, the social world and everything in it is but a poor imitation of its potential ideal self, and it is the role of the “enlightened” among us to point out that ideal and to help steer us toward achieving it. This is Bobby Kennedy’s “I dream things that never were and ask why not?” This is John Lennon’s “Imagine.” This is Obama’s “Fundamentally Transform.” This is Thomas Sowell’s “unconstrained” vision in which practically anything is possible. This is Plato’s “Light.”
Digging a little deeper, this algorithm incorporates the notion that the mind is a blank slate at birth, which means that everything we know about right and wrong is learned from formal education and from direct experience. It also means that differences among groups result solely from social constructs. The “good society” and the “new man” are therefore achievable simply by putting in place the right social constructs and teaching the right ideas. This operating system tends to seek radical, revolutionary change; throw out the entire existing system and create a whole new system based on “reason.” It puts mankind in the godlike position of “designing” social reality. It’s chief characteristic is epistemic confidence, even arrogance. It is, in short, social creationism.
The desire to improve society is also present in the operating system of the right, but it is tempered by reality. The social world is a complex system of nearly infinite size, and the capacities and capabilities of the human mind are limited. It is impossible for any single person or group of people to know all the facts (capacity), and even if it could, it does not have the processing power (capability) to sort out and reliably predict which inputs to the complex system will create what outputs. For this operating system, experience is the surest guide. It tends to seek gradual, incremental, change, achieving ever higher quality of life, one small step at a time, by standing on the shoulders of all who came before. This is Sowell’s “constrained” vision in which the possible is limited by reality. It’s chief characteristic is epistemic humility.