Mere priority affords no good ground for the exclusive right to an invention. The free exercise of thought is the common right of all. Wherefore if A excogitate a principle to-day, and B, by independent thought, excogitate the same principle to-morrow, both have an equal right to benefit by the discovery; and A has no natural right to debar B from the legitimate fruit of his intellectual effort. It may be even that A had no real priority of thought, but was only more knowing, more greedy, or was simply nearer to a patent office, and, though latest in arriving at the idea, was the first to secure a legal monopoly of its use. To found a right on such a race for priority is evidently irrational. The simultaneousness of discoveries and inventions by different minds, is a well-established fact in the history of science. Certain facts and reasonings, all tending in a given direction, are before the world. These act simultaneously on various minds, and produce in each the same development of thought. Now, with what justice do we pick out one of these many thinkers and give him a monopoly of the common thought? Nor is the injustice confined to the original idea, of which we grant a monopoly. By tying up one idea, we stop the whole course of thought in a given direction, and thus interfere generally, and to an indefinite extent, with the intellectual activity of other men. The inventor benefits by the ideas of the community, and has, therefore, no right to a special privilege for his idea. The universal thought of mankind is a common good; all benefit by it freely, and all are bound freely to contribute to it. Every thinker owes an incalculable debt to society. The inventor has the benefit of all foregone human thought, of all existing civilization. He has the unbought advantage of all laws, all language, all philosophy. He has the free use of all the methods and appliances, spiritual and material, which have been painfully elaborated by the thinkers and workers of all time. Why, then, should he alone have an exclusive privilege, in respect of the infinitesimal addition which he may make to the work of ages?