in advance 时间上 预先.
"when you pay in advance you receive a discount";
beforehand 除了有时间上 预先,超前外,还有非时间上 的,例如 “需要”上 预先,超前.另外有过早的意思.
She is always beforehand with the rent.她总是早早把租金准备好.
We were aware of the problem beforehand.我们事先就知道有这个问题.