 As Avicenna describes it, experience involves repeated sensation of some phenomenon that is preserved in memory, e.g., that purging of bile follows ingestion of scammony. It also involves a “hidden” or implicit process of reasoning. We infer that the repeated connection involves an essential relation between two things: e.g., it is not accidental that the purging of bile follows the ingestion of scammony, for regularities cannot be due to chance. This implicit process of reasoning removes doubt. So, experience gives rise to certitude. Avicenna defines certitude in terms of second-order belief: one is certain when one knows that what one has assented to cannot be otherwise (Black 2013b: 122). Certitude is not wholly subjective, since knowledge of a proposition requires its truth (Black 2013b: 125). On the other hand, though experience gives rise to certitude, it does not yield knowledge in the strict sense. For knowledge in the strict sense is both necessary and explanatory. From experience we derive our certitude that members of a certain species cause something; but experience does not show why (McGinnis 2003: 320–1).