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. 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.