In Promotions^x, Countable nouns^x, Nouns^x

Hi, How can we use the article "a" in front of words like "hello" and "thank-you" with or without quotation marks? If it has quotation marks around it, I take it as being treated as sort of an uncountable noun, but sometimes, I don't see quotation marks; then,...

Hi Prasanna, I have made some minor corrections in your essay. You seem to confuse the countable and non-countable nouns at times. History & mankind for example, are not countable. Wheras a rank, a promotion and the Wright Brothers are...