And so it seems probable that any mental image which happens to take hold on the mind, if not recognized as one of memory, or as corresponding to a fact in somebody else's experience, naturally assumes the form of an expectation of a personal experience.

The force of the expectation will vary in general as the vividness and persistence of the mental image.

Moreover, it follows, from what has been said, that this force of imagination will determine what little time-character we ever give to these wholly ungrounded illusions.
We see, then, that any process of spontaneous imagination will tend to beget some degree of illusory expectation.

And among the agencies by which such ungrounded imagination arises, the promptings of feeling play the most conspicuous part.

A present emotional excitement may give to an imaginative anticipation, such as that of the prophetic enthusiast, a reality which approximates to that of an actually perceived object.