As for ‘mind’, when substance has been rejected a mind must be some group or structure of events. … We might—though this would be rather unduly simple—define a ‘mental’ event as one which remembers or is remembered. Then the ‘mind’ to which a given mental event belongs is the group of events connected with the given event by memory-chains, backwards or forwards.

Bertrand Russell, History of Western Philosop…, loc. 2404