 There thus are different metaphysical views of theoretical entities in science, each of which is consistent with the understanding that a theoretical entity is inaccessible by means of unaided perception. First, theoretical entities are mind and language independent. Second, theoretical entities are mind and language dependent in some way or other. Third, they are conceived of as mathematical entities that are related to the observable world in certain determinate ways. We may thus distinguish between (i) a realist view, (ii) a collection of non-realist views and (iii) a Pythagorean view of theoretical entities.