{And they asked him} (kai (8872)(9374)(8873)an auton). Here the
paratactic kai is like the transitional oun (then). {What
then?} (Ti oun;). Argumentative oun like Paul's 	i oun in
 Ro 6:15 . _Quid ergo?_ {Art thou Elijah?} (Su Elias ei;). The
next inevitable question since Elijah had been understood to be
the forerunner of the Messiah from  Mal 4:5 . In  Mr 9:11f. 
Jesus will identify John with the Elijah of Malachi's prophecy.
Why then does John here flatly deny it? Because the expectation
was that Elijah would return in person. This John denies. Jesus
only asserts that John was Elijah in spirit. Elijah in person
they had just seen on the Mount of Transfiguration. {He saith}
(legei). Vivid dramatic present. {I am not} (ouk eimi). Short
and blunt denial. {Art thou the prophet?} (ho proph(8874)(8873) ei
su;). "The prophet art thou?" This question followed naturally
the previous denials. Moses ( De 18:15 ) had spoken of a prophet
like unto himself. Christians interpreted this prophet to be the
Messiah ( Ac 3:22  7:37 ), but the Jews thought him another
forerunner of the Messiah ( Joh 7:40 ). It is not clear in  Joh
6:15  whether the people identified the expected prophet with the
Messiah, though apparently so. Even the Baptist later became
puzzled in prison whether Jesus himself was the true Messiah or
just one of the forerunners ( Lu 7:19 ). People wondered about
Jesus himself whether he was the Messiah or just one of the
looked for prophets ( Mr 8:28  Mt 16:14 ). {And he answered}
(kai apekrith(885c)). First aorist passive (deponent passive, sense
of voice gone) indicative of apokrinomai, to give a decision
from myself, to reply. {No} (Ou). Shortest possible denial.