Likewise if every member of a group has the same thought, that is not a group idea: when all respond simultaneously to the same stimulus, it cannot be assumed that this is in obedience to a collective will. When all the men in a street run round the corner to see a procession, it is not because they are moved by a collective thought. Imitation indeed has a place in the collective life, it is one of the various means of coadaptation between men, but it is only a part and a part which has been fatally overemphasized.[11] It is one of the fruits of particularism. “Imitation” has been made the bridge to span the gap between the individual and society, but we see now that there is no gap, therefore no bridge is necessary. The core of the social process is not likeness, but the harmonizing of difference through interpenetration.[12] But to be more accurate, similarity and difference can not be opposed in this external way—they have a vital connection. Similarities and differences make up the differentiated reactions of the group; that is what constitutes their importance, not their likeness or unlikeness as such. I react to a stimulus: that reaction may represent a likeness or an unlikeness. Society is the unity of these differentiated reactions. In other words the process is not that merely of accepting or rejecting, it is bound up in the interknitting. In that continuous coördinating which constitutes the social process both similarity and difference have a place. Unity is brought about by the reciprocal adaptings of the reactions of individuals, and this reciprocal adapting is based on both agreement and difference. To push our analysis a little further, we must distinguish between the given similarity and the achieved similarity. The common at any moment is always the given: it has come from heredity, biological influences, suggestion and imitation, and the previous workings of the law of interpenetration. All the accumulated effect of these is seen in our habits of thinking, our modes of living. But we cannot rest in the common. The surge of life sweeps through the given similarity, the common ground, and breaks it up into a thousand differences. This tumultuous, irresistible flow of life is our existence: the unity, the common, is but for an instant, it flows on to new differings which adjust themselves anew in fuller, more varied, richer synthesis. The moment when similarity achieves itself as a composite of working, seething forces, it throws out its myriad new differings. The torrent flows into a pool, works, ferments, and then rushes forth until all is again gathered into the new pool of its own unifying. This is the process of evolution. Social progress is to be sure coadapting, but coadapting means always that the fresh unity becomes the pole of a fresh difference leading to again new unities which lead to broader and broader fields of activity.