 The third core Russellian monist thesis, quidditism about consciousness, states that quiddities are relevant to consciousness. More specifically, it states that quiddities are relevant to phenomenal consciousness. For example, consider the feeling one has when suffering from a painful migraine or when seeing a brilliantly red sunset. As it is often put, there is something it is like to have a phenomenally conscious experience (Nagel 1974; see the entry  consciousness;  throughout, all references to consciousness refer to phenomenal consciousness). There is no consensus among Russellian monists on exactly how quiddities are relevant to consciousness  (section 4).  But many claim that phenomenal properties are constituted by quiddities, or by quiddities together with various structural properties.