It is not difficult to discover such a law. We have but to look and we may see it. I do not pretend to give it scientific precision, but merely to point it out.
The incentives to progress are the desires inherent in human nature—the desire to gratify the wants of the animal nature, the wants of the intellectual nature, and the wants of the sympathetic nature; the desire to be, to know, and to do—desires that short of infinity can never be satisfied, as they grow by what they feed on.
Mind is the instrument by which man advances, and by which each advance is secured and made the vantage ground for new advances. Though he may not by taking thought add a cubit to his stature, man may by taking thought extend his knowledge of the universe and his power over it, in what, so far as we can see, is an infinite degree. The narrow span of human life allows the individual to go but a short distance, but though each generation may do but little, yet generations, succeeding to the gain of their predecessors, may gradually elevate the status of mankind, as coral polyps, building one generation upon the work of the other, gradually elevate themselves from the bottom of the sea.
Mental power is, therefore, the motor of progress, and men tend to advance in proportion to the mental power expended in progression—the mental power which is devoted to the extension of knowledge, the improvement of methods, and the betterment of social conditions.
Now mental power is a fixed quantity—that is to say, there is a limit to the work a man can do with his mind, as there is to the work he can do with his body; therefore, the mental power which can be devoted to progress is only what is left after what is required for non-progressive purposes.
These non-progressive purposes in which mental power is consumed may be classified as maintenance and conflict. By maintenance I mean, not only the support of existence, but the keeping up of the social condition and the holding of advances already gained. By conflict I mean not merely warfare and preparation for warfare, but all expenditure of mental power in seeking the gratification of desire at the expense of others, and in resistance to such aggression.
To compare society to a boat. Her progress through the water will not depend upon the exertion of her crew, but upon the exertion devoted to propelling her. This will be lessened by any expenditure of force required for bailing, or any expenditure of force in fighting among themselves, or in pulling in different directions.
Now, as in a separated state the whole powers of man are required to maintain existence, and mental power is set free for higher uses only by the association of men in communities, which permits the division of labor and all the economies which come with the co-operation of increased numbers, association is the first essential of progress. Improvement becomes possible as men come together in peaceful association, and the wider and closer the association, the greater the possibilities of improvement. And as the wasteful expenditure of mental power in conflict becomes greater or less as the moral law which accords to each an equality of rights is ignored or is recognized, equality (or justice) is the second essential of progress.
Thus association in equality is the law of progress. Association frees mental power for expenditure in improvement, and equality, or justice, or freedom—for the terms here signify the same thing, the recognition of the moral law—prevents the dissipation of this power in fruitless struggles.
Here is the law of progress, which will explain all diversities, all advances, all halts, and retrogressions. Men tend to progress just as they come closer together, and by co-operation with each other increase the mental power that may be devoted to improvement, but just as conflict is provoked, or association develops inequality of condition and power, this tendency to progression is lessened, checked, and finally reversed.