posted by rfvv .
1. Today is my birthday. One of my family members knew that. I have a sister. She gave me a watch for my birthday.
(Is this passage grammatical? Does it mean that she didn't give the watch on my birthday. She gave me a watch yesterday for my birthday. Am I right?)
2. She gave me a watch on my birthday.
3. She gave me a watch for my birthday.
(#2 mean she gave me a watch on March 13th, for example. However, In #3 mean she gave me a watch on March 13th or on March 12th or on March 14th. Is that right?)
In #1 and #3, "for my birthday" means that was the reason for the gift. It could have been given ON your birthday or ON another day, but it's not exact.
In #2, "on my birthday" is exact. It was given to you ON the exact day you celebrate your birthday.