The EL&U’s archives told me ‘thanks’ is slightly more informal than ‘thank you’. I’d like to get a little more specific info.
I’m now reading Harry Potter series and came across the following scene.
“Well, I just thought I’d congratulate you again on your splendid performance against that Horntail, Harry,” said Bagman. “Really superb.”
“Thanks,” said Harry, but he knew this couldn’t be all that Bagman wanted to say, because he could have congratulated Harry in front of Ron and Hermione. (Harry Potter 4 [US Version]: p.445)[Bold font is mine]
N.B.: Bagman is the head of a department of Magical Ministry and he is much older than Harry. They are acquainted with each other.
It seems to me that ‘thanks’ can be used in any occasion, even if the speakers are distant in their ages and social positions, but is there any occasion where the word isn’t appropriate? What makes you choose ‘thanks’ over ‘thank you’?
Also, can I use it for answerers and commentators in this site?
I often see ‘thanks’ this site, but I think they might be acquainted with each other in a chat or something. I tried writing ‘Hi, thanks’ a couple of times, but I can’t wipe off a feeling that I might be far too familiar and make people unpleasant.
Best Answer
I agree that "thank you" is slightly more formal than "thanks". I suspect if I was addressing the Queen I'd say "Thank you, ma'am". I tend to use "thank you" for emphasis, to show that I am really grateful, and it's not just a polite formality. Otherwise there's not a great difference, in my opinion of common usage. (Except for 'giving thanks', but that's a whole other kettle of fish.)