Abstract

According to a prominent thought, in one’s practical reasoning one should rely only on what one knows. Yet for many choices, the relevant information is uncertain. This has led Schiffer to the following objection: oftentimes, we are fully rational in reasoning from uncertain premises which we do not know. For example, we may decide to take an umbrella based on a 0.4 credence that it will rain. There are various ways proponents of a knowledge norm for practical reasoning can respond. One option is to say that the right way of dealing with uncertain information requires knowledge of probabilities. Another option is to say that credences can be knowledge because they really are beliefs with an unusual kind of content that consists of a set of probability spaces. Mixed accounts are possible as well. On neither of the accounts in the literature, however, can reasoning from uncertain premises be taken as reasoning based on a graded attitude, a credence, toward an ordinary proposition. To make room for this possibility, I argue that reliance comes in degrees. The knowledge norm is only plausible when taken to be concerned with full reliance.Partial reliance, on the other hand, goes hand in hand with credence.