I have two questions related to this topic. Since they are very closely related, I decided to group them in one thread. If it is better to separate them, please let me know and I will fix it. Thank you.
Context: It is only half a cup of milk. Drink it all.
Is it “half a cup of milk” or “half cup of milk”? I am leaning toward “half a cup of milk” but I have no explanation. I can only guess that it is probably because it is half of a cup, so half a cup. But then this reminds me of “half an hour” and “half hour” :( so now I have just confused myself.
Under the same context, except now instead of having “half a cup” we have “½ cup.”
Context: It is only ½ cup of milk. Drink it all.
Is it “½ cup of milk” or “½ a cup of milk”? I am pretty sure it is “½ cup of milk” because of examples like “⅔ cup of milk” and “½ cup of butter.” But again, I have no explanation (assuming I am right).
Please advise. Thank you in advance.
P.S. Under what grammar keyword should I look into for this topic? I thought it would fall into measure words or something, but my grammar book doesn't have this specific topic.