or 表示“否则”“要不然”时，既可连用陈述语气，也可接连用虚拟语气，主要看其隐含的是否是一个真实的条件：若是（或可能是）真实的条件，则用陈述语气；若不是真实的条件，则用虚拟语气。

▲连用陈述语气的例句：

Keep to the path or you'll lose your way. 沿这条小道走，否则就要迷路。（or=if you don’t keep to the path）

Turn your radio down, or you'll wake the neighbors. 把收音机的声音调小些，不然会把邻居吵醒。(or=if you don’t turn your radio down)

You’ve got to believe in yourself, or you’ll never succeed. 相信自己，否则你永远不会成功。(or=if you don’t believe in yourself)

▲连用虚拟语气的例句：

She had to have the operation, or she would die. 她必须动手术，要不然就没命了。(=or if she didn’t have the operation)

He studied hard, or he couldn’t have passed the exam. 他学习很努力，要不然他考试就不会及格了。(or=if he hadn’t studied hard)

I couldn’t remember her name, or I’d have introduced you. 我记不得她的名字，不然我就介绍你了。(or=if I had remembered her name)