general ideal by reference to which the real is to be estimated. It thus provides itself with a refuge iv CLOSED SOCIETY AND OPEN SOCIETY 233 in the Platonic theory, with the Idea of Good dominating all others: the reasons for action can then apparently claim to be ranged in order of merit beneath the Idea of Good, the best being those that come nearest to it, and the attraction of Good being the principle of obligation. But then the great difficulty is to say by what token we are to recognize that this or that line of conduct is nearer or further from the ideal Good; if this were known, it would be the essential, and the Idea of Good would become unnecessary. It would be equally hard to explain how the ideal in question creates an imperative obligation, especially the strictest obligation of all, the obligation which attaches to custom in primitive and essentially closed societies. The truth is that an ideal cannot become obligatory unless it is already active, in which case it is not the idea contained in it, but its action, which makes j it obligatory. Or rather it is only the name we give to the supposedly ultimate effect of that action, felt to be continu- ous, the hypothetical terminal point of the movement which is already sweeping us forward.J At the root of all theories, then, we find the two illusions we have time and again denounced. The first, a very general one,