The difference between artificial and natural objects seems immediately and unambiguously apparent to all of us. A rock, a mountain, a river, or a cloud "“ these are natural objects; a knife a handkerchief, a car "“ so many artificial objects, artifacts. Analyze these judgments, however, and it will be seen that they are neither immediate nor strictly objective. We know that the knife was man-made for a use its maker visualized beforehand. The object renders in material form the preexistent intention that gave birth to it, and its form is accounted for by the performance expected of it even before it takes shape. It is another story altogether with the river or the rock which we know, or believe, to have been molded by the free play of physical forces to which we cannot attribute any design, any project, or purpose. Not, that is, if we accept the basic premise of the scientific method, to wit, that nature is objective and not projective.
Hence it is through reference to our own activity, conscious and projective, intentional and purposive-it is as makers of artifacts-that we judge of a given object's "naturalness" or "artificialness." Might there be objective and general standards for defining the characteristics of artificial objects, products of a conscious purposive activity, as against natural objects, resulting from the gratuitous play of physical forces? To make sure of the complete objectivity of the criteria chosen, it would doubtless be best to ask oneself whether, in putting them to use, a program could be drawn up enabling a computer to distinguish an artifact from a natural object.
Such a program could be applied in the most interesting connections. Let us suppose that a spacecraft is soon to be landed upon Venus or Mars; what more fascinating question than to find out whether our neighboring planets are, or at some earlier period have been, inhabited by intelligent beings capable of projective activity? In order to detect such present or past activity we would have to search for and be able to recognize its products, however radically unlike the fruit of human industry they might be. Wholly ignorant of the nature of such beings and of the projects they might have conceived, our program would have to utilize only very general criteria, solely based upon the examined objects' structure and form and without any reference to their eventual function.
Chance and Necessity, 1971