The diverse opinions of Synesius, Orderic Vitalis, Gerald of Wales, Richard of Devizes, Jean Froissart, the monk of Leicester, Thomas à Kempis, Giles of Viterbo, Erasmus, John Whitgift, Macaulay, Ludwig Erichson, Ambrosio de Valencia, and Gordon Rupp on militant clerics are, in the end, personal opinions, no matter how eloquently expressed. While it is useful to know what Aquinas, Erasmus, and other writers thought about the great issues of their day, it is not enough to know what they thought, especially since so many others did not agree with them. It is much fairer to judge the clergy, at least in the first instance, by what the Church expects of them as expressed in its laws. Although it is widely assumed, even by ecclesiastical historians, that Roman Catholic canon law has always simply forbidden the clergy to bear arms under any circumstances, this has not been true since the twelfth and thirteenth centuries and is not true today. This chapter and the next will examine at several levels the evolution of the canonical ‘law of arms’ for the clergy through the High Middle Ages. It is an investigation not of what theologians and others believed the clergy ought to do, but rather of what ecclesiastical laws permitted, required, or forbade them to do.