 Most traditional versions of neutral monism were based on  (1),  the idea that the neutral is neither mental nor material. But occasionally the understanding of neutrality is informed by criterion (5): the neutral is that which is both mental and material. This view has been attributed to Thomas Nagel (Godfrey-Smith 2013: 1–2; Skrbina 2005: 237; but see also section  5.4).  That which is both mental and material is biased towards neither and hence neutral between them. In this way the both-interpretation captures an intuitive notion of neutrality. Moreover, (5) may tell us much more about the nature of the neutral entities than (1)–(4) do—just how much we learn about the nature of the neutral will depend on how the relevant concepts of the mental and the physical are fleshed  out.[2]