McGinn on experience of primary and secondary qualities
in terms of empirical properties and relations and without assuming his existence. It is in this way that we can, for example, describe the possible existence of the relation of absolute simultaneity. Absolute simultaneity is a relation such that, if it were to exist, it would be an equivalence relation among events, and it could be measured in the way that physicists once supposed. It is because no relation meets this description that we can conclude that no such relation in fact exists.