What grammatical function is や performing here?

Question

それで何だっけ?
昨日の夜の話
全然覚えてないや
「電話が鳴って君からだってわかったら
急に変な気分になったんだ。」

This is an excerpt of lyrics from Indigo la End's song 彼女の相談. I can't figure out what function the や in line 3 performs.

Does anyone have any input?

Answer 1

や at the end of a sentence has various meanings, but it's roughly categorized into two.

1. Kansai colloquial copula や (used in place of だ)
2. True sentence-end/interjectory particle や

Perhaps you'll see Kansai-ben's や more often, and it's discussed in many existing questions here:

• I don't understand what やな means at the end of a sentence...?
• The meaning of んや

But since や in your example comes right after ない, it's a sentence-end particle. (You cannot say ないだ, right?) It has several functions.

1. [after an i-adjective] Exclamation ("Oh", "Wow", sounds childish)

   すごいや！ Wow, it's great!
   ひどいや！ You're so cruel!

2. [after an imperative verb] Persuasion, urging ("Come on", "You", sounds masculine and rough) See: What does the word 「こいや」 mean? and What does the sentence ending particle や mean?

   飲めや。 Drink it.
   死ねや！ You, die!

3. [after an animate noun] Vocative ("Hey", "O", sounds old) See: What does や after someone's name mean exactly?

   シンデレラや、舞踏会に行きたいのかい？ Cinderella, do you want to go to the ball?

4. [usually after いい or ない] Indifference, giving up, reluctant acceptance ("Oh well", "Meh") See: Meaning of や in 「もうどうだっていいや」 and Help understanding いいやって and いやだなって

   それでいいや。 Well, that's okay (if not ideal).
   どうでもいいや。 Whatever. / Let it go. / I don't care.
   もう知らないや。 I don't care about it anymore.
   うーん、わかんないや。 Hmm, I don't know. / I give up.

5. [archaic; after a noun or an old adjective] Deep emotion, exclamation ("O", "Oh", "!", "...", poetic and old, typically seen in haiku) See: What is the function of 「や」 in this sentence? and Translation of うらめしや

   古池や蛙飛び込む水の音 (famous haiku)

In your case, や is used in the fourth sense. This や expresses the speaker is not particularly serious about 覚えていない(こと). In the lyrics, the woman is serious, but the guy doesn't even remember what they talked about yesterday.