We now, then, perceive how economics is a physical science. One of the most distinguished physical philosophers of the day expressed to me a doubt that economics is a physical science. But that all depends upon its fundamental conception and definition. So long as it was termed the "Production, Distribution, and Consumption of Wealth," there was nothing in the name or the nature of the subject to suggest any resemblance to a physical science; but as soon as we adopt the alternative and equivalent definition of the science as the science of commerce or exchanges, it is at once seen how it is a physical science, because there being three orders of exchangeable quantities, and therefore six species of exchanges, the object of the science is to discover the laws of the phenomena of these exchanges - that is, to determine the laws which govern their numerical relations of exchange. We have, in fact, a new order of variable quantities, and the laws which govern this new order of variable quantities must be in strict harmony with the laws which govern the relations of variable quantities in general. The laws which govern the variable relations of economic quantities must be in strict harmony with the laws which govern the varying relations of the stars in their courses. Like astronomy, economics is a pure science of ratios.

It is thus seen that economics is a distinct body of phenomena all based upon a single idea. Another great body of particulars is won from the vague, floating, and uncertain mass of knowledge - won from the void and formless infinite - and fixed and circumscribed by a definition which separates it from all other bodies of phenomena, and is therefore fitted to form a great demonstrative science of the same rank as mechanics, astronomy, optics, or any other physical science.

Thus it is clearly seen to be a physical science; but it is also a moral science, because its laws are based upon the mores - the of men. For we find that the same general laws of exchange or the principles of commerce hold good among all nations, among the rudest and the most civilised in all ages and countries. The laws of commerce are identically the same to-day as they were when commerce first sprang into being, and they will remain so to the end of time. The laws of commerce, said Edmund Burke, are the laws of Nature, and therefore the laws of God. That is why economics is a physical science, because it is based upon principles of human nature, which are as universal and as permanent as those upon which the physical substances are based. And therefore economics is a physical moral science, and the only moral science which is capable of being raised to the rank of an exact science.