I've posted a question about it a long while ago, so I'll copy the chosen answer here: "Why" is used as an expression to give the statement emphasis . "Why" can be replaced with something similar to "wow" in those examples. Why, thank you! = Wow! Thank you! "Why, yes. Didn't you know I was his cousin?" - In this case, "Why, yes" is more like "Yes, of course" (The "why" is said in front to give the sentence emphasis.) Why, no. I didn't know you were his cousin. Wow. No. I didn't know you were his cousin. ====================================== I liked what Eliot said in his comment: The second conversation is a bit difficult. Depending on where the emphasis is in each sentence, the meaning changes. Technically, the "why" shows some mild surprise, but in a humble way. It's rather old fashioned now to be humble in standard conversation. But in England we still use these forms of speech in the Houses of Parliament. ======================================= Here's the link if you want to know more about it: ttp://www.italki.com/answers/question/79081.htm

Porque yo quiero aprender español, yo hago la respuesta en español. El "why" en "why, thank you" enseña sorpresa. "Thank you" - Graciás "Why, thank you!" - "¡Anda! Graciás"

It is said to add emphasis. You'll see it often with an exclamation point: "Why, thank you!" In speech, it would also be be emphasized: "Why, THANK you!" I don't know where it originated, but it has been part of the English language for hundreds of years. It is not as popular as it once was, but it is still used a great deal.

Why = expression of surprise, and means something along the lines of: "You shouldn't have." "You are too good."

It's very difficult to explain WHY the "why" is there. It's just a way of adding a different tone to your "Thank you," but in no way changes the meaning.