Various arguments for (precise) probabilism assume that some relation or other is complete. Whether this is a preference over acts, or some “qualitative probability ordering”, the relation is assumed to hold one way or the other between any two elements of the domain. This hardly seems like it should be a principle of rationality, especially in cases of severe uncertainty. That is—to take the preference example—it is reasonable to have no preference in either direction. This is an importantly different attitude to being indifferent between the options. Mark Kaplan argues this point as follows: