German is taken in by Molly's revolutionary argument (9)
I believe the answer is:
syllogism
'argument' is the definition.
The definition and answer can be both related to thinking as well as being singular nouns.
Perhaps they are linked in a way I don't understand?
'german is taken in by molly's revolutionary' is the wordplay.
'german' becomes 'g' (abbreviation).
'taken in by' is an insertion indicator (back).
'revolutionary' says the letters should be written in reverse (letters revolve around).
'mollys' reversed gives 'syllom'.
'g'+'is'='gis'
'gis' put inside 'syllom' is 'SYLLOGISM'.
Can you help me to learn more?
(Another definition for syllogism that I've seen is " Deductive reasoning".)