Various social sciences, also, are needed to promote the welfare of mankind. Jurisprudence treats of the legal rights of persons, and how they may be best defined and secured by just laws. Political Philosophy inquires into the different forms of government and their relative advantages. Sanitary Science ascertains the causes of disease. The science of Statistics collects all manner of facts relating to the state or community. All these sciences are useful in showing how we may be made more healthy, wealthy, and wise. But #Political Economy# is distinct from all these other sciences, and treats of #wealth# itself; it inquires what wealth is; how we can best consume it when we have got it; and how we may take advantage of the other sciences to get it. People are fond of finding fault with political economy, because #it treats only of wealth#; they say that there are many better things than wealth, such as virtue, affection, generosity. They would have us study these good qualities rather than mere wealth. A man may grow rich by making hard bargains, and saving up his money like a miser. Now as this is not nearly so good as if he were to spend his wealth for the benefit of his relatives, friends, and the public generally, they proceed to condemn the science of wealth. But these complainers misunderstand the purpose of a science like political economy. They do not see that in learning we must do one thing at a time. We cannot learn the social sciences all at the same time. No one objects to astronomy that it treats only of the stars, or to mathematics that it treats only of numbers and quantities. It would be a very curious Science Primer which should treat of astronomy, geology, chemistry, physics, physiology, &c., all at once. There must be many physical sciences, and there must be also many social sciences, and each of these sciences must treat of its own proper subject, and not of things in general. #2. Mistakes about Political Economy.# A great many mistakes are made about the science we are going to consider by people who ought to know better. These mistakes often arise from people thinking that they understand all about political economy without studying it. No ordinary person of sense ventures to contradict a chemist about chemistry, or an astronomer about eclipses, or even a geologist about rocks and fossils. But everybody has his opinion one way or another about bad trade, or the effect of high wages, or the harm of being underbid by cheap labour, or any one of hundreds of questions of social importance. It does not occur to such people that these matters are really more difficult to understand than chemistry, or astronomy, or geology, and that a lifetime of study is not sufficient to enable us to speak confidently about them. Yet, they who have never studied political economy at all, are usually the most confident.