People agree, if not on paper (8)

I believe the answer is:

mentally

I'm a little stuck... Click here to teach me more about this clue!

'if not on paper' is the definition.
I can't judge whether this definition defines the answer.

'people agree' is the wordplay.
'people' becomes 'men' (men are people).
'agree' becomes 'tally' (synonyms).
'men'+'tally'='MENTALLY'

Can you help me to learn more?

(Other definitions for mentally that I've seen before include "by way of intellect" , "not in writing" , "in their heads" , "in the head" , "Intellectually" .)

I've seen this clue in The Globe and Mail.

Want a hint initially instead of a full solution? Install my app