Theory that alcohol is more than the sum of its parts? (6)
I believe the answer is:
holism
'theory' is the definition.
(I know that holism is a type of theory)
'alcohol is more than the sum of its parts?' is the wordplay.
'than the sum of its parts?' indicates a hidden word (part of the clue).
'HOLISM' is hidden within 'alcohol is more'.
'that' is the link.
(Other definitions for holism that I've seen before include "Medically, treatment of the whole person rather than symptoms" , "In medicine, treatment of the whole person rather than symptoms" .)