I think he is getting at the epistemological problem of first premises. If the only fact of epistemology that I accept is "I exist", the statement "Objective reality exists" cannot be proved.
I'm sure there's better formal language for this, but we could benefit by making a distinction between "facts in principle" and "facts in practice". Let's say a fact in principle is derived from a priori knowledge, whereas a fact in practice is one that we have accepted and depend on in order to make pragmatic decisions and survive. In principle, I believe that I exist but that I cannot prove objective reality exists. In practice, I accept that objective reality exists and that if I stand in front of a bus I will be hit.
I'm sure there's better formal language for this, but we could benefit by making a distinction between "facts in principle" and "facts in practice". Let's say a fact in principle is derived from a priori knowledge, whereas a fact in practice is one that we have accepted and depend on in order to make pragmatic decisions and survive. In principle, I believe that I exist but that I cannot prove objective reality exists. In practice, I accept that objective reality exists and that if I stand in front of a bus I will be hit.