双宾语及物动词buy后面如果直接跟了直接宾语，如果要引出间接宾语sb，必须使用介词for，不能用介词to。

(1)buy sb sth买给某人某物（属于双宾语结构）

Father bought me a new pen.
父亲给我买了支新钢笔。

We bought her a book.
我们给她买了一本书。

He bought her a new hat.
他给她买了一顶新帽子

(2)buy sth for sb为某人购买某物（属于单宾语结构）

She bought a tie for me.
她为我买了一条领带。

My father bought a dictionary for me yesterday.
我爸爸昨天为我买了一本字典。

“Here's a good shop, shall we try to buy a gift for mother?”
“这家商店不错,在这给妈妈买件礼物好吗?”