Can one use "Yet" at the beginning of a sentence as follows?
Yet, he came late.
Is this grammatical?
That should be like this, without a comma:
With random selections from Wolfe, Martin, and Tolkien, we have these examples:
There are function words in English which have different meanings according to their position in a sentence. "yet" is a good example. I suppose that etymologically we have two words of the form yet, yet1 and yet2.
yet1 is used in a sentence (negative or question) as in
1 Mother asking her little son: Is your brother up yet or is he still in bed?
Son: He isn't up yet.
In 1 yet is an adverb refering to the present time. I associate it with German jetzt (now).
yet2 has a totally different meaning. It is a conjunction (or better a sentence introduction) introducing a sentence that expresses an idea contrary to the statement in the preceding sentence.
2 A waiter of a small Italian restaurant about his job:
The pay isn't good. Yet it is a job.
This yet2 has the meaning of "but", but the contrast is expressed in a stronger way. I associate this yet2 with German jedoch (however).
OALD has separate entries for yet1 and yet2. Astonishingly etymonline explains only yet1, yet2 isn't mentioned.