Son has method to persuade (4)
I believe the answer is:
sway
'persuade' is the definition.
(synonyms)
'son has method' is the wordplay.
'son' becomes 's'.
'has' is a charade indicator (letters next to each other).
'method' becomes 'way' (I've seen this before).
's'+'way'='SWAY'
'to' is the link.
(Other definitions for sway that I've seen before include "Totter; influence" , "Pitch sideways" , "Power - rock" , "Move back and forth" , "Move from side to side; influence" .)