Probability or reasonable inference: should, ought
A more flexible degree of prediction is expressed by should and the less common ought. A driver might say, studying a map, ‘It should be easy to reach York from here’, glossed as ‘it is probably easy’. Here we have the notion of probability or what is reasonable to expect, based on deduction from facts known to the speaker.
There shouldn’t be any difficulties.
We should have enough petrol.
The main semantic feature distinguishing these modals from must and will is that they implicitly admit non-fulfilment of the predicated event, whereas must and will do not. We can say:
Where’s the map? It should /ought to be here in the glove compartment, but it isn’t, but not:
Where’s the map? *It must be here, but it isn’t.
We should /ought to have reached York by now , but we haven’t,
but not
*We must have reached York by now, but we haven’t.
The probability meaning of should and ought is sometimes merged with that of non-binding obligation, as in For this price, the hotel should be /ought to be much better, i.e. one would expect it to be better /it has the obligation to be better.
Likely and the noun likelihood, with the corresponding negative forms unlikely and unlikelihood, unambiguously express probability:
All flights are likely to be delayed.
There’s no likelihood of frost tonight.
The most likely outcome of Saturday’s match is a draw.
