Hume would have us believe that there are some beliefs to which we cannot doubt and be rational about such doubt.
Can I doubt that I exist? Descartes’ would say no; Kant would have a slightly more complicated story here. Hue would have us believe that the beliefs such as the external world, other minds, and perhaps, induction are such that we just simply believe them. These things we take not as self-evident, nor as desiderative of justification; but simply primitive facts that we take for granted.
Part of me can buy a story like this. The other part of me thinks; what about Transcendental deductions? It sounds like Kant is doing something more complicated than he may need to.
If the Kantian deduction fails, and, if we accept the Humean account has the same explanans, and we may take parsimony as a value; perhaps an account of natural belief may have an appeal.
We may talk of natural belief in various species; some, as an aspect of the workings of our mind, and others, as substantive content of our beliefs whereby we cannot but believe that such and such is the case; like ‘this is a table’, or ‘I am angry’. Those such propositions being the most obvious of our knowledge.
Some people worry that the idea of natural belief, and the consequence of it making (certain) sceptical worries powerless is dogmatism. I wonder if this may be true, but we are not to worry, for such dogmatism about the existence of the world is but a primitive that we must take for granted.