▲ It is not often that he comes late. 是个强调句。

原句是：He doesn't often come late. 有两个问题需要说明：

1. 这句话的not 不是否定come 的，而是否定often 的。

2. 大家知道，强调句除了句子的谓语动词以外，其他成分几乎都可以被强调，包括各种副词（时间副词、频度副词、地点副词）等。所以，频度副词often 也可以被强调。

▲ 网友的句子，属于强调句的否定句式。有些否定句在变成强调句时，要把否定词not 转移到被强调的词语之前。例如部分否定句，在变为强调句时，连同not 一起被强调，放在It is (was) 之后。“not… until…”句式被强调就是一个典型的例子，将not放在被强调的成分里面。例如：

All of the boys in our class don’t like football.

→It is not all of the boys in our class that (who) like football.

Both sisters are not interested in physics.

→It is not both sisters that (who) are interested in physics.

Everybody doesn’t know the answer.

→It is not everybody that knows the answer.

Money can’t buy everything.

→It is not everything that money can buy.

He didn’t realize his mistake until the teacher had told him.

→It wasn’t until the teacher had told him that he realized his mistake.

▲ 请比较以下两组，如果不把not放在被强调的成分中，强调的角度就不同。

A. It wasn’t I that made fun of him.不是我（而是别人）取笑他。

B. It was I that didn’t make fun of him. 就是我没有取笑他。

A. It wasn’t Mary that looked down upon you. 不是玛丽（而是别人）瞧不起你。

B. It was Mary that didn’t look down upon you. 就是玛丽没有瞧不起你。