Is לא necessary for this sentence? Can it be omitted and mean the same?
It seems from the first few examples that I was given, that שום can be either positive or negative, depending on context. (I first heard the word in a Hebrew song I heard which used the line "אני שום דבר"). Is that correct?
Since Hebrew uses double negative, shouldn't "I am nothing" be אני לא שום דבר ? Otherwise, why isn't there a double negative in this line?
No because it would "I am not nothing". I would say that in our sentence שום דבר is the subject so thats why we use לא
(For those not aware: the song is from ניקוי ראש Nikui Rosh, lit. ‘head cleaning’, Israel’s second ever satire show on TV. It was extremely influential, to the point people avoided planning events like weddings and bar mitzva celebrations when it was airing lest people didn’t come. Some of the actors on the show later became celebrated veteran actors. The song parodied in the middle is this jingle, advertising a brand of soaps, whose tune became so iconic every future ad for that brand has used a variation or a snippet thereof.)
So שום can be either garlic? I know that שום דבר is nothing. Is it like the word ביצה that can be egg such as swamp depending on context?
Well, these two homophones are not related. As is shown by Aramaic תּוּמָא garlic, this word had a proto-semitic [θ] like in thief, but שׁוּם is a secondary form of שֵׁם name, whose [ʃ] like in ship is original. By the way, בִּצָּה [bitsa] swamp and בֵּיצָה [be(y)tsa] egg sound different.