If, therefore, Political Economy be a science, it cannot be a collection of practical rules; though, unless it be altogether a useless science, practical rules must be capable of being founded upon it. The science of mechanics, a branch of natural philosophy, lays down the laws of motion, and the properties of what are called the mechanical powers. The art of practical mechanics teaches how we may avail ourselves of those laws and properties, to increase our command over external nature. An art would not be an art, unless it were founded upon a scientific knowledge of the properties of the subject-matter: without this, it would not be philosophy, but empiricism; [Greek: empeiria,] not [Greek: technae,] in Plato's sense. Rules, therefore, for making a nation increase in wealth, are not a science, but they are the results of science. Political Economy does not of itself instruct how to make a nation rich; but whoever would be qualified to judge of the means of making a nation rich, must first be a political economist. 2. The definition most generally received among instructed persons, and laid down in the commencement of most of the professed treatises on the subject, is to the following effect:--That Political Economy informs us of the laws which regulate the production, distribution, and consumption of wealth. To this definition is frequently appended a familiar illustration. Political Economy, it is said, is to the state, what domestic economy is to the family. This definition is free from the fault which we pointed out in the former one. It distinctly takes notice that Political Economy is a science and not an art; that it is conversant with laws of nature, not with maxims of conduct, and teaches us how things take place of themselves, not in what manner it is advisable for us to shape them, in order to attain some particular end.