It is true that he is a rather difficult phenomenon; his comings and goings are rather intermittent and fitful, his substance is too shadowy to be handled, and he has avoided hitherto equally the obtrusive inquisitiveness of the microscope and telescope.
A phenomenon which you can neither handle nor weigh, analyse nor dissect, is naturally regarded as intractable and troublesome; nevertheless, however intractable and troublesome he may be to reduce to any of the existing scientific categories, we have no right to allow his idiosyncrasies to deprive him of his innate right to be regarded as a phenomenon.

As such he will be treated in the following pages, with all the respect due to phenomena whose reality is attested by a sufficient number of witnesses.

There will be no attempt in this book to build up a theory of apparitions, or to define the true inwardness of a ghost.
There will be as many explanations as there are minds of the significance of the extraordinary narratives which I have collated from correspondence and from accessible records.

Leaving it to my readers to discuss the rival hypotheses, I will stick to the humbler mission of recording facts, from which they can form their own judgment.
The ordinary temper of the ordinary man in dealing with ghosts is supremely unscientific, but it is less objectionable than that of the pseudo-scientist.

The Inquisitor who forbade free inquiry into matters of religion because of human depravity, was the natural precursor of the Scientist who forbids the exercise of the reason on the subject of ghosts, on account of inherited tendencies to attribute such phenomena to causes outside the established order of nature.