Roman statesman uses co-author now and then (4)
I believe the answer is:
cato
'roman statesman' is the definition.
(I've seen this in another clue)
'co-author now and then' is the wordplay.
'now and then' means one should take alternating letters (letters taken on a regular basis, now and then).
'co'+'author'='coauthor'
The alternating letters of 'coauthor' are 'CATO'.
'uses' is the link.
(Other definitions for cato that I've seen before include "Roman statesman" , "Marcus Porcius - , Roman politician, censor" , "Senator" , "Ancient Roman censor" , "classical writer" .)