Full Idea
For Lewis, a belief mode is analysed by saying that to believe a content (analysed as a property) is for the subject of thought to 'self-ascribe' that property.
Gist of Idea
A content is a property, and believing it is self-ascribing that property
Source
report of David Lewis (Attitudes De Dicto and De Se [1979]) by François Recanati - Mental Files 18.3
Book Reference
Recanati,François: 'Mental Files' [OUP 2012], p.255
A Reaction
Lewis is weird. I would have thought you only self-ascribe the 'property' when you find yourself believing it. Lewis seems desperate to eliminate mental language. Belief can be a primitive concept without being primitive in ontology.