7. By protection_ism_ I mean the doctrine of protective taxes as a device to be employed in the art of national prosperity. The protectionists are fond of representing themselves as “practical” and the free traders as “theorists.” “Theory” is indeed one of the most abused words in the language, and the scientists are partly to blame for it. They have allowed the word to come into use, even among themselves, for _a conjectural explanation_, or _a speculative conjecture_, or _a working hypothesis_, or _a project which has not yet been tested by experiment_, or _a plausible and harmless theorem about transcendental relations_, or _about the way in which men will act under certain motives_. The newspapers seem often to use the word “theoretical” as if they meant by it imaginary or fictitious. I use the word “theory,” however, not in distinction from fact, but, in what I understand to be the correct scientific use of the word, to denote _a rational description of a group of coördinated facts in their sequence and relations_. A theory may, for a special purpose, describe only certain features of facts and disregard others. Hence “in practice,” where facts present themselves in all their complexity, he who has carelessly neglected the limits of his theory may be astonished at phenomena which present themselves; but his astonishment will be due to a blunder on his part, and will not be an imputation on the theory. 8. Now free trade is not a theory in any sense of the word. _It is only a mode of liberty_; one form of the assault (and therefore negative) which the expanding intelligence of the present is making on the trammels which it has inherited from the past. Inside the United States, absolute free trade exists over a continent. No one thinks of it or realizes it. No one “feels” it. We feel only constraint and oppression. If we get liberty we reflect on it only so long as the memory of constraint endures. I have again and again seen the astonishment with which people realized the fact when presented to them that they have been living under free trade all their lives and never thought of it. When the whole world shall obtain and enjoy free trade there will be nothing more to be said about it; it will disappear from discussion and reflection; it will disappear from the text-books on political economy as the chapters on slavery are disappearing; it will be as strange for men to think that they might _not_ have free trade as it would be now for an American to think that he might not travel in this country without a passport, or that there ever was a chance that the soil of our western states might be slave soil and not free soil. It would be as reasonable to apply the word “theory” to the protestant reformation, or to law reform, or to anti-slavery, or to the separation of church and state, or to popular rights, or to any other campaign in the great struggle which we call liberty and progress, as to apply it to free trade.