“Throughout any language, words of all kinds are always going personal to a certain extent: the subjective exerts a gravity-style pull on words’ meanings. Example: must started out in the objective command sense: You must stand still. Later came an alternate meaning of must, as in (doorbell rings) That must be the Indian food. In saying that, we don’t mean “I demand that that be the Indian food,” but a more personal, subjective sense of mustness. You mean that within your mind and your sense of what is likely, logic requires that you must suppose that it’s the Indian food, rather than the mail or a neighbor. First was the command meaning, objective and focused outward. But over time words often turn inward and become more about you. “That” (in my mind) “must be the Indian food”: here is psychology. Must got personal. Other times, things get so personal that the original meaning vanishes entirely. Here’s some Tennyson (sorry): Lancelot’s admirer Elaine is asleep “Till rathe she rose, half-cheated in the thought.” Rathe? Angry, as in “wrathed,” maybe? No, actually: the word meant “quick” or, in this passage, “early.” Elaine is up early with things on her mind. Rathe meant “early,” so rath-er, in Old and into Middle English, meant “earlier.” But a meaning like that was ripe for going personal, as must did. It happens via what we could call meaning creep, by analogy with the term mission creep—bit by bit, new shades creep into what we consider the meaning of something to be, until one day the meaning has moved so far from the original one that it seems almost astounding. What happened with rather is that something you’ve got going earlier or sooner is often something you like better. As such, if rather means “earlier,” then there’s an air about rather not only of sunrise, but of preferability. That is, to earlier English speakers, rather was as much about what you like better (something personal) as about the more concrete issue of what you do before you do something else. Today the relationship between the two meanings is clearer in sooner. In saying, “I’d sooner die than marry him,” you mean not that you’d prefer your death to precede your nuptials, but that you don’t want to marry the man in question.”