 Most extant versions of neutral monism seem to acknowledge that, in addition to the basic neutral entities, there exist derivative, non-basic, and non-neutral entities—mental and physical entities, for example. This raises the question about the relationship between these two kinds of entities. Every answer to this question faces two challenges. On the one hand there is the threat of elimination of the non-basic entities (see section  7.1);  on the other hand there is the threat that the non-basic, non-neutral entities turn into elements of ultimate reality, thereby putting an end to neutral monism.