Acton, however, wrote for a world which breathed in the atmosphere created by Kant. His position was something as follows: After the discovery of facts, a matter of honesty and industry independent of any opinions, history needs a criterion of judgment by which it may appraise men's actions. This criterion cannot be afforded by religion, for religion is one part of the historic process of which we are tracing the flow. The principles on which all can combine are the inviolable sanctity of human life, and the unalterable principle of even justice and toleration. Wherever these are violated our course is clear. Neither custom nor convenience, neither distance of time nor difference of culture may excuse or even limit our condemnation. Murder is always murder, whether it be committed by populace or patricians, by councils or kings or popes. Had they had their dues, Paolo Sarpi would have been in Newgate and George I. would have died at Tyburn. The unbending severity of his judgment, which is sometimes carried to an excess almost ludicrous, is further explained by another element in his experience. In his letters to Doellinger and others he more than once relates how in early life he had sought guidance in the difficult historical and ethical questions which beset the history of the papacy from many of the most eminent ultramontanes. Later on he was able to test their answers in the light of his constant study of original authorities and his careful investigation of archives. He found that the answers given him had been at the best but plausible evasions. The letters make it clear that the harshness with which Acton always regarded ultramontanes was due to that bitter feeling which arises in any reflecting mind on the discovery that it has been put off with explanations that did not explain, or left in ignorance of material facts.