dns header doubt

[Raghav S.N.]

hi folks,
i have some basic doubts regarding dns header.
as we know there are 2 flags Recursion desired(RD) and Recursion available
(RA) . RD is used by the client in any dns request and RA is used by the
server in the response. RD does not make any sense to server and RA for
client . so why 2 separate flags are used to denote these 2 requirements ?
couldnt it be managed by only one flag? what is actual reasons for keeping 2
separate flags instead of only one?
--
Raghav.S.N