You support the proposition of an individual! (6,6)
I believe the answer is:
second person
'you' is the definition.
(I've seen this before)
'support the proposition of an individual' is the wordplay.
'support' becomes 'second' (eg to second an idea is to support it).
'the proposition of an individual' becomes 'person' (I can't justify this - if you can you should give a lot more credence to this answer).
'second'+'person'='SECOND PERSON'
Can you help me to learn more?
(Another definition for second person that I've seen is " Category governing the addressee (gram.)".)