Se nur = If only, provided that.
Example.—Vi vidos Johanon, se nur vi alvenos frue = You will see John, provided that you (will) arrive early.
Se okaze = If perchance, in case, in the event of.
Example.—Se okaze vi venus malfrue, Johano ne estus tie ĉi = If perchance you should come late, John would not be here.
Se tamen = If however, if still, if though, if notwithstanding.
Example.—Se tamen vi ne povos veni morgaŭ matene, venu vespere = If, however, you are not (will not be) able to come to-morrow morning, come in the evening.
Sed = But.
Example.—Li legas, sed ne komprenas tion, kion li legas = He reads, but does not understand what he reads.
Sed ankaŭ = But also.
Example.—Ŝi donis al mi ne nur hundon, sed ankaŭ ĉevalon = She gave me not only a dog, but also a horse.