 The new science of mathematical probability had come into being on the continent just around the time that Locke was writing the Essay. His account of probability, however, shows little or no awareness of mathematical probability. Rather it reflects an older tradition that treated testimony as probable reasoning. Given that Locke’s aim, above all, is to discuss what degree of assent we should give to various religious propositions, the older conception of probability very likely serves his purposes best. Thus, when Locke comes to describe the grounds for probability he cites the conformity of the proposition to our knowledge, observation and experience, and the testimony of others who are reporting their observation and experience. Concerning the latter we must consider the number of witnesses, their integrity, their skill in observation, counter testimony and so on. In judging rationally how much to assent to a probable proposition, these are the relevant considerations that the mind should review. We should, Locke also suggests, be tolerant of differing opinions as we have more reason to retain the opinions we have than to give them up to strangers or adversaries who may well have some interest in our doing so.