 Lewis’s main argument for the Ability Hypothesis can be summarized like this. (1) The only alternative to the Ability Hypothesis is what he calls the Hypothesis of Phenomenal Information (HPI). (According to the HPI knowing what it is like is propositional in the following sense: coming to know what it is like involves the elimination of hitherto open possibilities). (2) The HPI is incompatible with physicalism. (3) The Ability Hypothesis is compatible with physicalism and explains everything that may be explained by the HPI. Therefore: The Ability Hypothesis should be preferred.