but, however: a weighty turn that sets what follows squarely against what was just said
Hebrew has plenty of light ways to say "and" or "but." This is not one of them. It is a heavy word, almost always standing first in its clause, and it announces that a real objection is coming rather than a passing qualification. Ten of its nineteen appearances are in the book of Job, where it is the sound of one debater cutting straight across another.
What holds its uses together is the shape of the move rather than its content. Something has just been said, and the speaker refuses to let it stand as the last word. That is why one word can carry a flat contradiction ("but his younger brother shall be greater"), a personal counter-position ("but as for me, I would seek God"), and an oath sworn against a doubt ("but as surely as the LORD lives"). In every case the ground shifts under what came before.
The shift can also be quiet. Twice a storyteller uses the word to slip in a correction about a place name, noting that the town had been called something else all along. Nobody is arguing there, yet the logic is the same: the account just given is not the whole account.
Hebrew's other emphatic words do different work. One of them (אָכֵן), usually rendered "surely," insists on what is actually the case when someone has it wrong. Another (אַךְ), usually rendered "only" or "however," narrows a statement down to less than it claimed. This word neither corrects a fact nor trims a claim; it plants a whole counter-claim beside the one just made.