But mass-action in which critical thought is not a concurrent item never is wholly safe. It is least dangerous in play-activities in which the many actually play, not merely look on; it is most perilous when a whole population, or a class in society, or a party, acts as a unit under the inspiration of some high sentiment, religious, patriotic, or other. For now concentration of mind upon a given end that stirs deep emotion not merely postpones thought, but controls thought. The mind is now ready to affirm or deny anything whatever in the interest of its consuming passion; or, if ‘interest’ rather than ‘passion’ is the type of control, unlimited ingenuity is employed in digging out evidence that we are already acting wisely and fairly. At this point the problem of release of our powers takes this form: How are the functions of thought to be performed and made effective where men act in groups, societies, classes, and masses? A special phase of this problem concerns the method of rational action where conflict arises or is threatened between two sets of persons. A phrase that has been coming into use recently, “cooperative thinking” points the way to a solution, the only possible solution, of this problem. There are two aspects of it. One is “thinking” in the strict sense of active inquiry by analytic methods; the other is “cooperation” as contrasted, on the one hand, with thinking in solitude, and on the other hand, with the strife-and-victory attitude and habit. Such thinking is, of course, not an invention, nor a new discovery. It exists in circles of friends who muse by the fireside without desire to win victories over one another; it exists in some families and partnerships, in which the members pool their views and thereby attain harmony of action; it characterizes the old Quaker type of deliberation in which there was much silence and listening, but freedom to speak, with the final word of the chairman (no vote having been taken), “It seems to be the sense of the meeting that ...”; it can be witnessed in assemblies in the interest of scientific research, when each participant in discussion takes the attitude of inquiry. What has to be done with this already old experience of thinking together is threefold: To extend the practice from these restricted groups to other groups and to the larger aggregations of men; to extend it from the few interests in which it is now recognized to all interests that call for corporate action; and to dig deeper into the nature and the conditions of cooperative thinking, particularly in areas of conflict, and to improve the technic of it.