  However, if the primary parts of reality are persons and the relation of determining correspondence is the relation of perception, then McTaggart holds that every substance can have a sufficient description even though every substance is  gunky.[31] Since it is possible that every spiritual substance be both gunky and have a sufficient description, idealism is a live option. That it is possible does not show conclusively that it is actual, but according to McTaggart, absent any better hypothesis, it is the one that is reasonable to accept. McTaggart holds that we can conceive of nothing that is not a material object, a sense-datum, or something spiritual, and since the first two kinds of objects are metaphysically impossible, the hypothesis of idealism is the only conceivable hypothesis left standing.