Thank you you

NO IT IS NOT A SENTENCE BECAUSE THERE IS NO SUBJECT, VERB AND OBJECT.
I AM A BOY. IS A SENTENCE BECAUSE SUBJECT IS I , VERB IS AM, AND BOY IS OBJECT.

2014-06-24 14:05:37 補充：
THANK YOU IS ONLY A KIND OF GREETINGS, NOT A SENTENCE.GOOD MORNING IS ALSO NOT A SENTENCE BECAUSE THERE IS NO SUBJECT,VERB AND OBJECT.

2014-06-24 23:39:27 補充：
THANK YOU 知足常樂
In simple terms, a sentence is a set of words that contain:
a subject (what the sentence is about, the topic of the sentence)
a predicate (what is said about the subject)
Look at this simple example:
<----- sentence ----->
subject predicate
verb
You speak English.

2014-06-24 23:41:24 補充：
更正：SENTENCE未必一定要OBJECT.
不過THANK YOU沒有SUBJECT，所以不是SENTENCE.

Thank you. It can be a sentence with the implied subject 'I'.

Thank you is a sentence

Yes. It is.
Coz it's a kind of exclaimation of the end of the speech.

Yes. It is a sentence, but not in the form of S + V + O.

Other examples include:

"Go away!"

"Good morning."

2014-06-24 18:08:03 補充：
謝謝 Happy 的意見，也請看看：

http://www.englishclub.com/grammar/what-is-a-sentence.htm

2014-06-25 18:10:55 補充：
如果根據以上連結，

Go away 是 sentence 因為隱藏了 You 這個 subject，

那麼用同樣的邏輯，可否理解

Thank you 是 sentence 隱藏了 I 這個 subject？

我也不確定，但值得討論一下。