I try penal reform. Others subscribe to it (5,4)
I believe the answer is:
party line
'others subscribe to it' is the definition.
I can't judge whether this defines the answer.
'i try penal reform' is the wordplay.
'reform' is an anagram indicator (letters in a new form).
'i'+'try'+'penal'='itrypenal'
'itrypenal' anagrammed gives 'PARTY LINE'.
Can you help me to learn more?
(Other definitions for party line that I've seen before include "what politician follows" , "Political policy to which all must subscribe" , "Official policy" , "politicians are expected to follow?" , "more than one can call on" .)