One view or glimpse of the former, has the same effect as several of the latter.
But they are not only possible evils, that cause fear, but even some allowed to be impossible; as when we tremble on the brink of a precipice, though we know ourselves to be in perfect security, and have it in our choice whether we wili advance a step farther.

This proceeds from the immediate presence of the evil, which influences the imagination in the same manner as the certainty of it would do; but being encountered by the reflection on our security, is immediately retracted, and causes the same kind of passion, as when from a contrariety of chances contrary passions are produced.
Evils, that are certain, have sometimes the same effect in producing fear, as the possible or impossible.

Thus a man in a strong prison well-guarded, without the least means of escape, trembles at the thought of the rack, to which he is sentenced.

This happens only when the certain evil is terrible and confounding; in which case the mind continually rejects it with horror, while it continually presses in upon the thought.

The evil is there flxed and established, but the mind cannot endure to fix upon it; from which fluctuation and uncertainty there arises a passion of much the same appearance with fear.
But it is not only where good or evil is uncertain, as to its existence, but also as to its kind, that fear or hope arises.