thank
(adj.) thankful (unthankful); (n.) thankfulness
thank作为及物动词，常用搭配是thank sb (for sth / for doing sth)，如：
She said goodbye and thanked us for coming.
thank表示“感谢”，习惯上只接“人”作宾语，而不能接“事”作宾语：
正：Thank you for your help.
误：Thank your help.
另外的用法：
1. have sb to thank for (doing) sth 归功于，如：
I have my parents to thank for my success.
2. thank your lucky stars 感谢你的幸运之星，口语中用于表达幸运，尤其是躲过了不愉快或危险的事。如：
Just thank your lucky stars you weren't in the house at the time.
appreciate
(adj.) appreciative (inappreciative); (n.) appreciation
appreciate作为“感激”解释时是及物动词，常用搭配：appreciate doing sth，后跟动名词或代词it代指的事情。习惯上只能接“事”作宾语(object)，而不能接“人”作宾语：
正：I'd appreciate some help.
误：I'd appreciate you for some help.
appreciate也指“欣赏”，有“对某事物有一定的兴趣及认识”的含义，如：
In time you'll appreciate the beauty and subtlety of this language.
此外，在商业书信来往中，appreciate一字出现率颇高，但其意和上面提及的“欣赏”音乐有所不同；如：
We greatly appreciate your getting the goods to us at such short notice.
在这句里，“We greatly appreciate...”和“Thank you for...”含意相同。
appreciate的第三个意思是“（对一种情况或问题的）理解”，如
I fully appreciate your concern. We will do all in our power to help.
appreciate的另一用法是指某东西“增值”，是不及物动词，如：
Their investments have appreciated over the years.
大家有没有留意到appreciate解作升值时是不需接宾语(object)的？
grateful
（反）ungrateful; (n.) gratitude (ingratitude)
grateful没有相应的动词，它的常用搭配是be grateful to sb for sth，或者后面跟不定式或that从句，如：
I am extremely grateful to all the teachers for their help.
She seems to think I should be grateful to have a job at all.
He was grateful that she didn't tell his parents about the incident.
另外，grateful也可用于表达请求，这种用法在书信或者其他正式场合用得比较多，如：
I would be grateful if you could send the completed form back as soon as possible.
除了上述的用法区别之外，thank, appreciate和grateful在表达情感上也有略微的区别：
"When you are 'grateful' to someone, you can sometimes feel a little 'beholden' to them. It creates a feeling of 'owingness'." 也就是说grateful带有一点“义务”的性质。
而另一方面，"When we appreciate someone or something there is a feeling of ending. There is a feeling of finality. We do not feel the need to pay this person back." 当我们用appreciate有点意味着这件事的结束，不需要再做什么回报。
另外，oblige (vt.) 一词也有“使感激”的意思，如：
I'm much obliged to you. 我非常感谢你。
不过oblige更常见的含义是“迫使”，如：
Parents are obliged by law to send their children to school.
