This book is the third of the series dealing with man's bodies, its two predecessors having been The Etheric Double and The Astral Body. In all three, identically the same method has been followed; some forty volumes, mostly from the pens of Dr. Annie Besant and Bishop Leadbeater, have been carefully searched for data connected with the mental body; those data have been classified, arranged and presented to the student in a form as coherent and sequential as the labours of the compiler have been able to make it.

Throughout this series no attempt has been made to prove, or even to justify, the statements made, except insofar as their own internal evidence and reasonably justify them. The bonafides of these veteran investigators and teachers being unquestionable, the results of their investigations and their teachings are here set out, without evasion or reservation of any kind, so far as possible in their own words, modified and abridged only where necessary to suit the requirements of an orderly and logical presentation of the subject-matter.

The question of proof is an entirely separate issue, and one, moreover, of vast dimensions. To have attempted to argue or prove the statements made would have defeated the primary object of these books, which is to lay before the serious student a condensed synthesis, within reasonable compass, of the teachings from the sources named regarding the bodies of man and the planes or worlds to which these belong. Those who desire proofs must search for them elsewhere.

Arthur Edward Powell (1882-1969), was a Theosophist whose books were published beginning in the early 1900s. He studied the major esoteric works of Helena Blavatsky, Charles Webster Leadbeater and Annie Besant.