 Now consider (4). It is commonly thought that (4) is necessarily true. For example: a substance composed overwhelmingly of atoms that do not contain 79 protons in their nuclei could not be gold. But (4) does not on its face look like a conceptual truth: it was a substantive discovery that there were protons at all, let alone how many protons an atom of gold characteristically possesses. Further (4) does not seem like it reflects a law of nature in the way that (3) does: rather, (4) seems to follow immediately from facts about what it is to be gold. Examples like (4) thus purport to give us an initial grasp on metaphysical modality as distinct from the other modalities considered thus far.