One assumes the Holy Grail holds that everything we know can be well connected into a complete whole. History is against us here because it always discovers something we did not know before that modifies what we know now. We can always vary a definition, or use negation. Godel's proof makes clear one cannot justify or rationalise the assumptional labels an argument is based on, in whichever evidential ways. At exactly the juncture where the argument encroaches on its assumptions it turns vague and ambiguous again.
Cosmology suffers that problem too about the size and duration of our universe.
For any paradigmatic closure exludes a paradox or more, as does too the speed of light for Relativity, as we get close enough to it. The mind brain problem is therefore undecidable. Thus we may name undecidables for which neither observation not discourse can settle matters, except by assumption, as null categories. Scientific evidence is not philosophical evidence. Another label would be scalar, as it cannot be measured, nor, in that case, can it be well defined.