Informed, we think, on revolutionary (2,3,4)
I believe the answer is:
in the know
'informed' is the definition.
(I've seen this before)
'we think on revolutionary' is the wordplay.
'revolutionary' indicates an anagram.
'we'+'think'+'on'='wethinkon'
'wethinkon' is an anagram of 'IN THE KNOW'.
(Other definitions for in the know that I've seen before include "Possessing private information" , "Privy to special information" , "Informally, having inside information" , "Having been informed" , "well-informed" .)