It is of no use studying the question of the attitude of the mediæval Church towards heresy unless one is prepared to use imagination enough to envisage heresy from the mediæval point of view. Men’s mental outlook is governed by the intellectual conditions of their own day. A few individuals may be, as the phrase goes, ‘in advance of their time’; but at the best they form only a small minority. To consider abstractly the rights and wrongs, the advantages and disadvantages of institutions and systems is the function of the philosopher. But the historian, while not ignoring the abstract question, has specifically the function of ascertaining what, in point of fact, people’s opinions have been and why they formed them. Much that has been written on the subject of religious toleration is of only limited validity because it simply denounces, and does not attempt to explain or to appreciate, the psychology of intolerance.[479] Thus, for example, Locke’s ‘Letters on Toleration’ have little _argumentative_ value, because they are based on a complete _ignoratio elenchi_. Religious toleration is a great principle, but many modern dithyrambs on the inalienable right of liberty of thought and conscience fall rather wide of the mark, can convince only the already converted. It is not very profitable to bring forward the theory of the indefeasible right of free thought in condemnation of mediæval society—to the whole of which, and by no means to its clerical elements only, the conception of such a right was entirely foreign. After all, even to-day the belief in an absolute toleration is held by only a very few, and even these anarchists will usually be found to hold it with certain reservations.[480] Organized society cannot tolerate the forces which are subversive of it. It does not tolerate the criminal. ‘A universal and absolute toleration of everything and everybody would lead to a general chaos as certainly as a universal and absolute intolerance.’[481] It is undoubtedly true that a certain measure of ‘intolerance is essential to all that is, or moves, or lives, for tolerance of destructive elements within the organism amounts to suicide.’[482] The individual possesses rights in so far as they are not prejudicial to the welfare of his fellows and the interests of the entire community. And the recognition that the maintenance of social order was perfectly compatible with the acknowledgment of the right of individual opinion and the permission of diversity of views, this in the Middle Ages ‘was a discovery to be made, not a truth to be proved.’[483]