The aim of this book is to investigate the question, What bearing, if any, does what is called "mystical experience" have upon the more important problems of philosophy? We start with a psychological fact the denial of which could only proceed from ignorance. Some human beings do occasionally have unusual experiences which come to be distinguished as "mystical".
These are recorded, or at least referred to, in the literatures of most advanced peoples in all ages.
But since the term "mystical" is utterly vague, we must first examine the field empirically to determine what types and kinds of experience are called mystical, to specify and classify their main characteristics, to assign boundaries to the class, and to exclude irrelevant types.
We then ask whether these experiences, or these states of mind, so selected and described, throw any light on such problems as the following: Whether there is in the universe any spiritual presence greater than man; and if so, how it is related to man and to the universe in general; whether we can find in mysticism any illumination on the questions of the nature of the self, the philosophy of logic, the functions of language, the truth or untruth of human claims to immortality, and finally the nature and sources of moral obligation and the problems of ethics generally.
I write as a philosopher, and not as a mystic.
It should be emphasized that in so difficult a field we cannot expect "proofs," "disproofs," "refutations," "certainties." The mystic indeed does not argue. He has his inner subjective certainty. But this only raises a new and puzzling problem for the poor philosopher. At any rate, the utmost we can expect in this area is tentative hypotheses, reasonable opinions. And of course only nonscientists believe in the supposed certainty of science. Scientists know that their solutions are hypothetical only; and ours will doubtless be much more so.