The Golden Bough [excerpt]

..."So natural is the knowledge and belief of the soul's existence and immortality that we find traces of it in all ages, and among nations even the most barbarous. This must have originated in the soul's conscious feelings of her own existence, - a sort of crude conception of her own being and qualities. Men saw that her powers continued paramount amidst the successive changes of our material frame, and thence drew references of immortal existence. But, strange as it may appear, as men have advanced in Science, they have retrograded in certainty regarding the nature and qualities of the soul, and its primitive substance. The Epicureans considered it to be a suitable air, composed of atoms in primitive corpuscles. The Cartesians made thinking the essence of the soul, and thus deduced its immateriality and immortality. But Spinosa, who maintains that nothing exists beside matter, asserts the soul to be of the same substance with the body.
Now I have sometimes tried to side with the sage, on the ground of the obvious certainty that the soul grows and expands with the body's growth and strengthens with her strength - dwindling away again in drivelling and palsied age to a mere withered stem of the once glorious mental flower. But I found that this theory will never do - at least it would never do for me; as it destroyed all the fine fairy visions which I had so long entertained of the soul's separate existence: not after death, for that I never presumed to call in question; but in deep sleep, in trances and all the other standings - still of the corporeal functions, it is well known that I have always maintained that the soul rooms at large, and by that means views scenes and draws conclusions predictive of future events.
Indeed, the soul in human nature seems to be all in all. Its various states of changeful feelings direct all the body's motions and affections. It is the soul that makes the body what it is; and in a future state of existence the same soul will still make the same individual being, of whatever component parts its body may be composed..."

~ Sir James Frazer (on the perils of the disembodied soul)