这两个动词均含“购买”之意。
buy : 普通日常用词，既可指日常随意购物也可指大的购买。
- Eventually she had saved enough money to buy a small car.
她最终存够了买一辆小汽车的钱。 - He bought his mother some flowers/He bought some flowers for his mother.
他给母亲买了些花。 - There are more people buying at this time of the year so prices are high.
这个季节购物的人比较多，所以价格高。 - The company was set up to buy and sell shares on behalf of investors.
成立该公司为的是代表投资者买卖股票。 - I bought my camera from a friend of mine.
我的相机是从一个朋友处买的。
purchase : 正式用词，指大宗购货或购买重要东西。无感情色彩，强调物品的购得。
- Tickets must be purchased two weeks in advance.
门票必须提前两周购买。 - Except under clearly defined circumstances, it is illegal in Britain for a company to purchase its own shares.
在英国，除非是在明确规定的情况下，否则一个公司购买自己的股票是违法的。 - She purchased her first house with the money.
她用这笔钱买了她的第一栋房子。
