The following are not among the least puzzling remarks in Wittgenstein's Philosophical Investigations:

572. Expectation is, grammatically, a state; like: being of an opinion, hoping for something, knowing something, being able to do something. But in order to understand the grammar of these states it is necessary to ask: ‘What counts as a criterion for anyone's being in such a state?’ (States of hardness, of weight, of fitting.)

573.… What, in particular cases, do we regard as criteria for someone's being of such and such an opinion? When do we say: he reached this opinion at that time? When he has altered his opinion? And so on. The picture which the answers to these questions give us shews what gets treated grammatically as a state here.