Take some flat tiles. Arrange them together to cover a small area. If you live in a flat place, you can make the resulting surface quite large. As you are of human size, it will not be possible to notice that the local impression of flatness contrasts with the large-scale properties of the Earth, which is approximately spherical, and hence not flat.
Take some uncontroversial propositions as premises. Combine them and reason deductively to arrive at new propositions. If your starting premises are rich, you can generate a large set of related propositions related to the first by deduction. These, too, appear uncontroversial, and compel agreement. A recondite theorem by Kurt Gödel assures you that there are macroscopic properties of the set of propositions that are “uncontroversial” that you will not encounter in your purely local reasoning.
Reasoning is always local: from these propositions to those. Rationalists believe that reasoning delivers certainty, and is a fine basis for belief. But if we look at the application of reasoning in all domains, we find bizarrely incompatible belief sets. Where these belong to exotic others, we interpret them as superstition, religion, culture, anything but reason. Our reasoning, so it goes, should not be prey to such pollution. Yet in the most exotic and incompatible cultures, we still find the clothes of reason; arguments are built with premises and conclusions. The premises, we say, are no longer uncontroversial. Those others do not seem to be aware of the limits of their reasoning.
Within contemporary Western scientific discourse, every attempt is made to keep out the spooks of religion, the chimera of mere culture, and the fabrications of fantasy, we seem to detect in the exotic others. But in discussion of human individuals, or persons, there arises a peculiar entity, the psychological subject, to whom agency is attributed, and with which we identify. We quibble about its exact makeup and constitution, even its location, but it would be very upsetting to discover that it might be no more real than Krishna, Gabriel, Satan or Mary Poppins. For if it were to be banished, we should no longer be able to establish meaningful premises that referred to our valued selves.
Discussion of the person sometimes refers to a body, but more frequently, and importantly, it refers to the locus of feelings, sentiments, and experience. Attempts to naturalise the presumed domain of experience have led to such unstable suggestions as the equation of the activity of brain with “mind”. The presumption of a cognitive system that causally gives rise to actions is another such attempt. Phenomenological perspectives share the belief of neurophysiological reductionists that there is a one-person domain of lived experience that could, in principle, be naturalised.
Lurking underneath all such efforts is some kind of P-world assumption that is tied to the notion of the present moment, the here-and-now for a subject, in which qualia exist, arising from sensorimotor embedding in a world. Time, and the relation between subject and world, are inextricably intertwined. Furthermore, the P-world is conventionally held to be distinct from, and prior to, the fabric of conceptual structure required to imbue the human world with stable entities and forms of organisation.
But the agent with its P-world is, itself, a pre-theoretic assumption of a kind with the pre-theoretic assumptions of other cultures. It is a Protestant, post-Enlightenment creation, upon which we have founded legal systems, ethical systems, states, and our (not-so) modern world.
When we recognize this, and accept that some such assumption will always underlie our discussions about ourselves, we see that we need to place bounds on rationality. It does not extend everywhere. We will always have to have discussions with others whose beliefs, no matter how scientifically schooled, are radically different from our own. This requires diplomacy. We need to learn to speak with caution.