since, yet

Both of these words are adverbs expressing time but doing so in different ways and meanings. Since can mean (1) "at some past time," "before now" (She has long since forgotten me); (2) "between then and now" (He has since left town); (3) "from some time in the past up until now" (She came last week and has been making trouble ever since). The word until is usually superfluous in a since phrase: "He had not voted since 1972 until this fall" can better be expressed "He had not voted from 1972 until this fall." Yet means (1) "at this time" (Don't go yet); (2) "thus far" (The signal had not yet come); (3) "still" (Something is yet to be done); (4) "in addition" (yet another time); (5) "nevertheless" (poorer yet wiser). Because both since and yet cover time up to the present, an accompanying verb should be in the perfect, not past, tense: "There has been no agreement on the dispute that has prevented progress since the meeting began." "Have you written to her yet?" "Did you eat yet?" is nonstandard."Have you eaten yet?" is standard. See also ago.