Having now given the three great facts on which the science is founded, it becomes necessary to fix precisely the terms to be used in the further development of these inquiries. Political economy is unlike all other sciences in this, that it has not the option of making or choosing its own terms. From the nature of the case, it is obliged to adopt words in common use. It is encumbered with all the notions, false or loose, which may have been attached to these. It has to speak of wealth ; of value and utility; of labor and capital; of production, exchange, distribution, and consumption. These are common phrases. Each has a variety of meanings in popular language ; yet, when used in the discussion of this science, it must have one meaning as definite, exclusive, and precise as the terms of natural history. The liability to confusion from this source can only be guarded against by being kept constantly in mind. Until the proper definitions become instinctive, so that they arise freely in their own shapes on the mention of such terms, there will be a constant slipping back, as it were, to their habitual meanings in common life. At the best, the laborious reference of the mind to formal definitions will tend to diminish the force of all representations and arguments where they appear. The greatest obstacle, however, encountered by writers, is not that arising through popular prepossessions in regard to words ; but it is their own misapplication of language, confounding things essentially distinct, and clothing exact principles in expressions so vague and indeterminate as to make science impossible.

We have said that political economy treats of wealth; but what is wealth? In popular language, it is houses, lands, ships, merchandise, with a general "and so forth," — all that we call property. In science, the term "wealth" includes all objects of value, and no other.

A discussion of its principles will be satisfactory only so far as the explicitness and exclusiveness of this term is held in view. No apology is to be given for the definition, and no substitute offered. The least deviation from this line will lead to ceaseless entanglements and perplexities.

The principle is cardinal. The science turns on it.

Political economy has been called the "science of values."

No definition could be more strictly accurate; but we shall retain that already given, as being more popular, and as nearer to the customary use of the words. It is, then, the science of wealth, understanding that wealth consists of objects of value only.