‘Skin for skin,’ said a certain evil one, ‘yea all that a man hath will he give for his life,’ and the proverb is true (with a modification) as regards the life of the soul, no less than as regards that of the body. Take away all hope of a future state,—appear to demonstrate, if not with absolute certainty, yet with an approach to it, that such a condition of things is antagonistic to well-understood scientific principles, and we feel certain that the effect upon humanity would be simply disastrous. At any rate, those who propound an argument of this kind must reasonably expect determined opposition from the followers of religion. Let us here, before proceeding further, take the opportunity of stating that we discuss only the _physical_ aspects of the argument regarding a future state. Being neither metaphysicians nor moral philosophers, we leave to others more competent than we can be the argument which may be based upon the universal craving among the intelligent races of mankind for a life beyond the grave. In the fourth and following editions of our work, while we have not materially altered our argument, we have recast to some extent the shape in which it was first put before the reader, and this recasting has taken a more definite form in our present edition. The large amount of friendly criticism which our work has called forth has convinced us that we did not at first sufficiently separate between certain conclusions which inevitably flowed from our argument, and certain others which, while deriving their strength from a totally different quarter, were yet not inconsistent with the former, but even, it might be, supported by them. The consequence has been that we have found ourselves credited with attempts which were very far from our thoughts, such, for instance, as the endeavour to deduce Christian theological doctrine from mere physical considerations. We have therefore thought it desirable to bring in review before the reader, in this introductory chapter, the fundamental points of our argument, more especially as in what follows we may not always be able without an undesirable formality to keep separate the foundation and the superstructure. * * * * *