Full Idea
It is often held to be a consequence of the rationalist conception of substance, that separate substances cannot interact (since causal interaction is a form of mutual dependence).
Clarification
'Substances' are thought of as the underlying basis of existence and identity
Gist of Idea
The very concept of a substance denies the possibility of mutual interaction and dependence
Source
Roger Scruton (Modern Philosophy:introduction and survey [1994], Ch.16 n)
Book Reference
Scruton,Roger: 'Modern Philosophy: introduction and survey' [Sinclair-Stevenson 1994], p.539
A Reaction
Yes, substances seem incapable of interaction, just as Leibniz argues that perfections could never interact. They are too pure.