Epistemology is the study of how people should form credences about the nature of the world. 

Beliefs and credences are purely evaluative attitudes: they are simply about the way that we think the world is. A person might believe that it will rain, for example, even though they hope that it will not.

Beliefs are all-or-nothing attitudes: we either believe that it will rain or we don't believe that it will rain. Credences, on the other hand, reflect how likely we think it is that something is true, expressed as a real number between 0 and 1. For example, we might think that there is a 80% chance that it will rain, and therefore have a credence of 0.8 that it will rain.

It is widely held that beliefs are rational if they are supported by our evidence. And credences are rational if they follow the probability axioms (e.g. a credence should never be greater than 1 in any event) and are revised in accordance with Bayes’ rule.

Improving the accuracy of beliefs

One way to improve a person’s capacity to do good is to increase the accuracy of their beliefs. Since people’s actions are determined by their desires and their beliefs, a person aiming to do good will generally do more good the more accurate their beliefs are.

Examples of belief-improving work include reading books, crafting arguments in moral philosophy, writing articles about important problems, and making scientific discoveries.

Two distinctions are relevant in this context. First, a person can build capacity by improving either their factual or their normative beliefs. Second, a person can build capacity by improving either particular beliefs or general processes of belief-formation.