Page:Philosophical Review Volume 13.djvu/577

563 be regarded as essential conditions in reference to certain phenomena. Take, for instance, the question as to the age of the earth upon which we live. The geologist tells us that at least two hundred millions of years are required; the physicist, on the other hand, tells us that the life of the sun cannot be stretched to nearly that number of years. Lord Kelvin says: "It would, I think, be exceedingly rash to assume as probable anything more than twenty million years of the sun's light in the past history of the earth, or to reckon more than five or six million years of sunlight for time to come." Such radical difference of opinion naturally gives us pause when we undertake to state just what can and cannot come to pass in regions and ages which lie wholly beyond our ken. If we cannot easily interpret the past when we have the data before our eyes, how can we expect to interpret the future or the far remote when we are precluded from knowing so vast an amount of the data.

Mr. Wallace no doubt would take exception to our strictures upon his argument on the ground that the progress of science has been so uniform and so comprehensive as to determine quite definitely the essential conditions which must be fulfilled in order that living organisms should be produced and preserved. In the marvelous advance of knowledge, however, we have as yet before us great and undiscovered countries whose outskirts we have not commenced to penetrate. What is known of the potential properties of matter, and the forces of nature whose operations are still undisclosed? Is our scientific knowledge such as to set a necessary limit to the nature and scope of such forces, should they be discovered? We think not. The difficulty of interpreting comprehensively any known conditions, even of the simplest nature, should deter us from too dogmatic conclusions concerning hypothetical relations under unknown conditions.

Moreover, it is quite impossible for us to know certainly that mind manifests itself only through the medium of brain structure central to a highly developed living organism. There may be other forms which intelligible beings assume in the outer confines of the universe. This is, of course, merely conjectural; nevertheless, the mere possibility of unknown forms, through whose media thought may find expression, should cause us to hesitate in our inferences as to what does, and what does not, transcend the sphere of the possible, or even of the probable.