Let us, then, consider the powers of the ordinary man first, and let us take as examples of them those powers or faculties which are most universally distributed amongst the human race—namely, the powers by which the rudest populations obtain enough food to live upon. Now such faculties, practically universal as they are, would be potential only, not actual, if it were not for two things. These are certain appetites or desires, having a physiological origin, on the one hand, and the external conditions on the other, which make the satisfaction of those appetites, or the fulfilment of those desires, a possibility. Thus if men could live without eating, and had no desire for food, those special faculties would be dormant which are now exercised in agriculture; and this means that for all practical purposes they would not exist at all. These faculties would also not exist at all, no matter what men’s desire for food might be, if the whole of the earth’s crust had {273} happened to be cast-iron, and if tillage were consequently impossible, and there were no seeds to sow. In other words, the very commonest and very simplest faculties which human beings possess have a practical and a universal existence in those beings, only because, in the first place, they minister to universal wants, and because, in the second place, the earth is so constituted as to supply the materials on which these faculties can operate. Or, to put the matter in more general terms, the very commonest and simplest faculties are not practically self-existent, except as mere barren potentialities; and as practical forces they exist only in the degree to which they are evoked by external things and circumstances—by some external object, such as food, which excites and will satisfy desire, and by external circumstances which make the object obtainable.