Full Idea
Leibniz held that dualism of mind and body is an illusion and that both are really the same thing, and that this thing is mind.
Gist of Idea
Leibniz said dualism of mind and body is illusion, and there is only mind
Source
report of Gottfried Leibniz (works [1690]) by R Martin / J Barresi - Introduction to 'Personal Identity' p.22
Book Reference
'Personal Identity', ed/tr. Martin,R /Barresi,J [Blackwells 2003], p.22
A Reaction
I am puzzled by this, as Leibniz is famous for the view that mind and body are parallel. See idea 5038, and also 2109 and 2596. Monads are, of course, entirely mental, and are the building blocks of reality. Clearly I (and you) must read more Leibniz.
Related Ideas
Idea 5038 Assume that mind and body follow their own laws, but God has harmonised them [Leibniz]
Idea 2109 Increase a conscious machine to the size of a mill - you still won't see perceptions in it [Leibniz]
Idea 2596 Maybe mind and body are parallel, like two good clocks [Leibniz]