Even in the rather fantastic realm of ghosts, the stories fall into regular groups, advancing in difficulty, like exercises in music or in a foreign language.

We therefore start from the easiest Exercises in Belief, or even from those which present no difficulty at all.

The defect of the method is that easy stories are dull reading.

But the student can "skip".

We begin with common every-night dreams.
Sleeping is as natural as waking; dreams are nearly as frequent as every-day sensations, thoughts, and emotions.