but

before 900; Middle English buten, Old English būtan for phrase be ūtan on the outside, without. See by¹, out

1. But, however, nevertheless, still, yet are words implying opposition (with a possible concession). But marks an opposition or contrast, though in a casual way: We are going, but we shall return. However indicates a less marked opposition, but displays a second consideration to be compared with the first: We are going; however ( “notice this also” ), we shall return. Nevertheless implies a concession, something which should not be forgotten in making a summing up: We are going; nevertheless ( “do not forget that” ), we shall return. Still implies that in spite of a preceding concession, something must be considered as possible or even inevitable: We have to go on foot; still ( “it is probable and possible that” ), we'll get there. Yet implies that in spite of a preceding concession, there is still a chance for a different outcome: We are going; yet ( “in spite of all, some day” ), we shall return. 2. See except¹.

1. But, like and, is a common transitional word and often begins sentences. When it is used in the middle of a sentence as a coordinating conjunction like and or so, it is not followed by a comma unless the comma is one of a pair setting off a parenthetical expression: His political affiliations make no difference, but his lack of ethics does. The cast is nearly complete, but, our efforts notwithstanding, we lack a star. See also and, so¹.
2, 10. When but is understood as a conjunction and the pronoun following it is understood as the subject of an incompletely expressed clause, the pronoun is in the subjective case: Everyone lost faith in the plan but she ( did not lose faith ). In virtually identical contexts, when but is understood as a preposition, the pronoun following it is in the objective case: Everyone lost faith but her. The prepositional use is more common. However, when prepositional but and its following pronoun occur near the beginning of a sentence, the subjective case often appears: Everyone but she lost faith in the plan. See also doubt, than.