Taking knowledge as a starting point › Evidence Is What You Know

Chapter 9 defends the equation commonly written as E = K: a subject's total evidence consists of the propositions that subject knows. This concerns the subject's body of evidence, not the claim that every known proposition supports every hypothesis. Williamson also distinguishes what belongs to one's evidence from the relation of its supporting some further proposition. His discussion appears in “Evidence,” especially sections 9.1–9.3.

Return to the report. You may know that the receipt displays a particular reference number, that the submission page opened, and that your colleague received a notification. These propositions can support a further conclusion about successful submission. A confident but false belief that the report was accepted cannot itself belong to your evidence under E = K. A different true proposition, that the screen displayed an acceptance message, might belong to your evidence if you know it.

That distinction keeps the proposal from demanding that inquiry begin with certainty about every conclusion. We can know observations while remaining uncertain about what explains them. We can also use a known fact about probabilities as evidence without knowing which uncertain outcome will occur. An investigator can reason from what is known while exploring a hypothesis that remains unproved.

The controversial step is identifying all evidence with knowledge. A critic can ask whether a careful but deceived observer has evidence for a false conclusion. Williamson's framework permits that observer to know some things, including facts about appearances, while denying that every apparent fact belongs to their evidence. An internalist critic may regard this as giving too little weight to the observer's perspective. The disagreement concerns what evidence is, rather than whether deception can be convincing.