请看下面这三种情形：

　　Ⅰ 现在简单时态

　　⒈现在简单时态可以用来表示未来的动作或活动，但这活动必须事先已有计划，如：　
　　● The plane to Hawaii leaves at 10 tonight.
　　● The British Prime Minister arrives at 8 tomorrow morning.

　　这样的不寻常时态里的动词通常只限于“来”和“往”之类的活动，不是任何动词都适用。

　　⒉现在简单时态也可用来取代时间副词分句（adverb clauses of time）或条件副词分句（adverb clauses of condition）中的现在未来时态，如：　
　　● Let's wait until all the guests come.
　　● If it rains tomorrow, we can't go fishing.

　　理论上可以说“until all the guests will come”和“if it will rain tomorrow”，但实际句子里，并不如此。

　　⒊现在简单时态有时可以用来代替现在过去时态，使所叙述的事物更现实、更灵活，如：　
　　● Alexander Pope says, “A little learning is a dangerous thing.”
　　● The Chinese proverb has it, “God helps those who help themselves.”

　　只有在特殊情况下，才用这种时态；否则，过去的事， 只好用过去时态，比较妥当。

　　Ⅱ 现在进行时态

　　⒈现在进行时态可以用来表示未来的节目或已策划的活动，如：　
　　● They are going downtown this afternoon.
　　● I am seeing an old friend tonight.

　　⒉现在进行时态，也和副词“always, continually, constantly”等连用以表示不断重复的举动，言下有不胜其烦之感，如：　
　　● Janet is always complaining.
　　● Why are you continually finding fault with our new system?
　　● Strange! The weather here is constantly changing.

　　Ⅲ 过去简单时态

　　⒈过去简单时态可用来表示目前不易实现的假设或愿望，如：　
　　● lf I were you, I would join that activity.
　　● I wish I had better luck next time.

　　⒉过去简单时态也可以用来代替现在简单时态，以表示礼貌，如：　
　　● Could you tell me how to go to the library?
　　● I would appreciate it if you could help me.
　　● Would you mind lending me your pen for a while?

　　上述寻常时态的不寻常用法，如果用得恰当，肯定可以增添英语的灵活性。