Full Idea
The 'disjunctive' theory of perception says that we have either veridical perception or else hallucination, but there is no common element in the form of a 'perceptual experience' which would be present in either case and merely caused in different ways.
Clarification
'Veridical' means true; 'disjunctive' means either/or
Gist of Idea
The 'disjunctive' theory of perception says true perceptions and hallucinations need have nothing in common
Source
E.J. Lowe (Introduction to the Philosophy of Mind [2000], Ch. 6)
Book Reference
Lowe,E.J.: 'Introduction to the Philosophy of Mind' [CUP 2000], p.145
A Reaction
McDowell is associated with this view. It seems to be another attempt to get rid of sense-data. It seems odd, though, to say that a hallucination of a dagger has nothing in common at all with experience of real daggers. Why did hallucinations evolve?