For the past century and a half, metaphysics (the philosophy of ultimate assumptions concerning the nature of reality) has been ignored, ridiculed, asserted to be unnecessary; and the philosophical focus has been on epistemology - that is, the question of knowledge (how we can known anything, or know any specific thing).
Thus, it has been common since Logical Positivism for modern thinkers to claim - incoherently - that do not have any metaphysical assumptions, but 'instead' base their beliefs on 'evidence' (thereby including the assumption that they already-know what counts as valid evidence and they already-know to interpret it validly...).
Anyway - we should acknowledge that metaphysics is necessary, and an explicit metaphysics is necessary in modernity because metaphysics Will Be Challenged.
So - anyone can state a basic assumption, something about which we say: It Just Is; and the proper question is how may metaphysical assumptions be evaluated?
Ultimately personal evaluation is an intuitive process, by which our true-self (our real-divine self) grasps the proposition entire and makes a solid evaluation. But that comes at the end of a process of clarification - that is, we need to come to that state of simplicity and clarity before we can evaluate it as-a-whole.
One help is to assume the truth of the assumption, then ask: Does this assumption make sense of the fact that I know it?
(In other words, does this metaphysics support a coherent epistemology?)
If the assumption is (assumed to be) true,
Then could we, personally, know-that it was true?
Many metaphysical assumptions cannot sustain an epistemology by which they could be known.
This would incline me to reject them - how about you?
Most mainstream metaphysical assumptions are incoherent wrt. epistemology. As examples:
If natural selection is assumed metaphysically true, as the only and sufficient explanation of Man; then human reason must be a product of natural selection; which means that human reason can never know anything (because natural selection is about differential fitness, not about truth).
If it is assumed that the universe is assumed to be a combination of randomness and determinism; then we personally could never know this - because we personally would be a combination of randomness and determinism and could never know anything. The universe might actually Be random/ determined - but if so, we personally could never know that.