Full Idea
'Socrates and killing are two' would be an illegitimate sentence according to the doctrine of types.
Gist of Idea
The theory of types makes 'Socrates and killing are two' illegitimate
Source
Bertrand Russell (My Philosophical Development [1959], Ch.14)
Book Reference
Russell,Bertrand: 'My Philosophical Development' [Routledge 1993], p.119
A Reaction
This nicely shows how Ryle's notion of a 'category mistake', although it is a commonsense observation of bogus reasoning, arises out of Russell's logical analysis of sets. Of course, the theory of types has its critics.