Accepted by party members, he provides hypotheses (8)
I believe the answer is:
theories
'hypotheses' is the definition.
(I know this)
'accepted by party members he' is the wordplay.
'accepted by' indicates putting letters inside (inserted letters are accepted).
'party members' becomes 'tories' (I am not sure about this - if you are sure you should believe this answer much more).
'tories' placed around 'he' is 'THEORIES'.
'provides' is the link.
Can you help me to learn more?
(Other definitions for theories that I've seen before include "Assumptions" , "General principles or opinions" , "Conjectures" , "Abstract principles" , "Explanatory suppositions" .)