David Hume became a radical skeptic of all truth claims first by arguing that whatever can’t be discovered using science is blind speculation, unknowable, and irrationally believed. He then discovered that most scientific knowledge is itself acquired using non-scientific philosophical assumptions and became skeptical of it too (such as all inductive knowledge, ‘scientific’ laws, and causation).
I think David Hume was right. All is unknowable, unless there is revelation. Attempts to find a sufficient ground for genuine knowledge on unaided human reason –that is, apart from divine revelation — will ultimately reduce to non-knowledge (skepticism, irrationality, egoism). But that hardly fits human experience. We have knowledge. But how is that knowledge justified? It can’t be, if there is no absolute personal God.
The late philosopher Dr. Greg Bahnsen used this line of argumentation (genuine human knowledge of any kind presupposes the existence of transcendental abstract entities including the laws of science, morality, and logic, which in turn presuppose the existence of an absolute personal God such as that which Christianity provides).
Here’s a link to his classic debate with Gordon Stein (atheist, committed to empiricism).