Full Idea
The supervenience [of mental characteristics on the physical] might be taken to mean that there cannot be two events alike in all physical respects but differing in some mental respect, or an object cannot differ mentally without altering physically.
Gist of Idea
Supervenience of the mental means physical changes mental, and mental changes physical
Source
Donald Davidson (Mental Events [1970], I)
Book Reference
Davidson,Donald: 'Essays on Actions and Events' [OUP 1982], p.214
A Reaction
This is the first occasion on which Davidson introduced his notion of supervenience. Supervenience is often taken to be one-way. The first implies physical causing mental; his second implies that mental causes physical.