Without bees, the crops can't continue to grow.

Without bees 仍然是“含蓄条件”，但含蓄条件和虚拟语气没有必然的联系。

书上说的是“含蓄条件虚拟语气句”。意思是说，有时虚拟语气的使用是因为里面包含着“含蓄条件”。这不等于说，有含蓄条件就必然使用虚拟语气。

在含有 if 条件句的复合句中，一般通过主、从句的谓语动词形式，即可判断出是否用了“虚拟语气”。但很多情况下，虚拟的条件并不是直接通过条件句来表示，而是用一些词、短语或其他连词，甚至通过上下文的暗示，这就是所谓的含蓄条件。

有时候还有更含蓄的，句子主语本身就是一种含蓄条件。例如：

1. Any thinking person would not accept such a condition.

任何一个有思想的人都不会接受这个条件。

等于说：If he were a thinking person, he would not accept such a condition.

2. A wiser man would not have done such a foolish thing.

聪明一点的人是不会干出这等蠢事的。

等于说：If he had been a wiser man, he would not have done such a foolish thing.

3. Only a scientist could understand all that this pursuit meant.

Only a scientist 存在含蓄条件，这句话蕴含着这层意思：

An ordinary person can’t understand all that this pursuit meant. He could understand all that this pursuit meant only if he were a scientist,

一个普通人无法理解这种追求的全部含义。只有是一名科学家，他才能懂得这种追求的全部意义。

以下也是“含蓄条件”，但比较明显。虚拟的条件并不是直接通过条件句来表示，而是用一些词、短语或连词，如，without, but for, otherwise, or, but, but that 等方式体现出来，甚至上下文暗示。这种句子叫含蓄条件虚拟句。

    Without air，there wouldn't be living things in the world.

    →If there were no air，... 没有空气，世界上就没有生物。

    She would have come to see you，but she was so busy that day.

    →If she had not been so busy that day，she would have come to see you.

    她本来会来看你的，可是那天她实在太忙了。

    Such mistakes could have been avoided.

    →If we had been more careful, such mistakes could have been avoided.

    （如果我们再仔细一些）这样的错误本来是能够避免的。

    But for your advice，I would have failed.

    →If you hadn't given me advice，I would have failed.如果不是你的建议，我会失败的。

    He came to town yesterday，otherwise/or I would not have met him.

    →If he hadn't come to town yesterday, I would not have met him.

    他昨天到城里来了，不然我就不会遇见他了。

    You would be a fool to refuse his offer.

    →If you should refuse his offer, you would be a fool.

    你要是拒绝他的提议，就太傻了。

He reminded me of what I would otherwise have forgotten.

幸亏他及时提醒我，要不然我就忘了。

We must care for the weak who would otherwise fall by the wayside. 

我们要关心那些弱者, 不然他们会因失败而放弃努力的。

我分成两句，就好理解了：

He reminded me of that, otherwise, I would have forgotten it.

We must care for the weak, otherwise they would otherwise fall by the wayside.