 However, if co-ownership is necessary, is it also sufficient? It seems that is is possible for items that are not unified with one another to be simultaneously presented to one and the same subject. This seems to happen, for example, in split brain cases, or fictional variations thereof—e.g., Parfit’s example of a single subject who is able simultaneously to try out two alternative approaches to solving a math problem (1984: 246–248). This state of affairs would seem to be a case of parallel but nonunified sets of conscious states had by the same subject, in some good sense of the term ‘same subject’. The same would seem to hold of the contents of a subject who switches back and forth between lobes who lacked memory of earlier contents. If so, co-ownership would appear not be sufficient for unity. A fortiori, co-ownership would appear not to capture what is distinctive about unified consciousness. Put differently, if there is a requirement here of any kind, more than co-ownership seems to be needed. The subject must have a certain kind of relationship to the material. As Kant put it, the material must be something to the subject (A116)—and this requires a subject to whom things can be something. Mere ownership by itself would appear to fall short (Brook 1994: 135–9, discusses these issues in connection with Kant).