Full Idea
We can't take a statement that two men, whose overt behaviour was not actually different, were in different states of mind as being really a statement that the behaviour of one man would have been different in hypothetical circumstances that never arose.
Gist of Idea
You can't define real mental states in terms of behaviour that never happens
Source
Peter Geach (Mental Acts: their content and their objects [1957], §3)
Book Reference
Geach,Peter: 'Mental Acts: Their content and their objects' [RKP 1971], p.6
A Reaction
This is the whole problem with trying to define the mind as dispositions. The same might be said of properties, since some properties are active, but others are mere potential or disposition. Hence 'process' looks to me the most promising word for mind.