Doubts are back, ideas follow (6,8)
I believe the answer is:
second thoughts
'doubts' is the definition.
(I've seen this before)
'back ideas follow' is the wordplay.
'back' becomes 'second' (synonyms).
'ideas' becomes 'thoughts' ('thought' can be a synonym of 'idea').
'follow' is a charade indicator (letters next to each other).
'second'+'thoughts'='SECOND THOUGHTS'
'are' acts as a link.
(Other definitions for second thoughts that I've seen before include "Change of mind" , "change of heart" , "revised opinion" , "Doubts; reconsideration" , "change of plan" .)