Forces simple changes (6)
I believe the answer is:
impels
'forces' is the definition.
('impel' can be a synonym of 'force')
'simple changes' is the wordplay.
'changes' indicates an anagram.
'simple' with letters rearranged gives 'IMPELS'.
(Other definitions for impels that I've seen before include "Urges forward" , "Urges or drives to do something" , "Forces, urges to action" , "Drives or forces" , "Drives on in simple way" .)