“in the synagogue.” The record of Jesus casting a demon out of a man in the synagogue at Capernaum is in Mark 1:23-28 and Luke 4:33-37.
“spirit (that is to say an unclean demon).” This construction in Greek is the genitive of apposition (Cp. Lenski). The literal Greek, “a spirit of an unclean demon,” means, “a spirit, that is to say an unclean demon,” or “a spirit, namely, an unclean demon,” or even, “a spirit—an unclean demon.” To us today it seems strange to say, “A spirit—an unclean demon,” because to us all demons are “unclean” and evil, but we must remember that in the theology and thinking of the Greco-Roman world, not all “demons” were evil. Like people, some were good and some were bad, and also like people they were capable of doing good in one circumstance but then evil in another. [For more information on the use of demons in the Greco-Roman world, see commentary on Acts 17:18].