Kant introduced this distinction, which he called the distinction between phenomena and noumena. Phenomena are objects as they appear to us. Noumena are what exist independently of our cognition and thus are inaccessible to us. But science has arguably meddled with phenomena, and it has succeeded, so noumena feel useless to a scientist. I think a scientist may even go further and say there is no noumena at all—only phenomena and phenomena which we have not accessed yet. I think the key behind this claim is the (reasonable) assumption that any distinction between things in nature can always be represented as a distinction in sense impressions or concepts, at least indirectly, with the aid of instruments. There is no distinction between things in nature that cannot in principle, be mapped to distinctions in sense impressions. I’ll call this the representability principle: For any real distinction in nature, there exists in principle a corresponding distinction in possible sense impressions or conceptual representations, possibly mediated by instruments. 

Kant may now say, “You cannot rule out the possibility of distinctions that never affect appearances.”- to which this Immanuel will reply, “While that is true, that's as speculative as saying the negation of it—but the negation is useful and productive, unlike the original statement.”