Though those different plans were, perhaps, first introduced by the private interests and prejudices of particular orders of men, without any regard to, or foresight of, their consequences upon the general welfare of the society; yet they have given occasion to very different theories of political economy; of which some magnify the importance of that industry which is carried on in towns, others of that which is carried on in the country. Those theories have had a considerable influence, not only upon the opinions of men of learning, but upon the public conduct of princes and sovereign states. I have endeavoured, in the fourth book, to explain, as fully and distinctly as I can, those different theories, and the principal effects which they have produced in different ages and nations.

To explain in what has consisted the revenue of the great body of the people, or what has been the nature of those funds which, in different ages and nations, have supplied their annual consumption, is the object of these four first books. The fifth and last book treats of the revenue of the sovereign, or commonwealth. In this book I have endeavoured to show, first, what are the necessary expenses of the sovereign, or commonwealth; which of those expenses ought to be defrayed by the general contribution of the whole society; and which of them by that of some particular part only, or of some particular members of it: secondly, what are the different methods in which the whole society may be made to contribute towards defraying the expenses incumbent on the whole society, and what are the principal advantages and inconveniences of each of those methods: and, thirdly and lastly, what are the reasons and causes which have induced almost all modern governments to mortgage some part of this revenue, or to contract debts, and what have been the effects of those debts upon the real wealth, the annual produce of the land and labour of the society.