both vs. all 辨析

先看例句：

1. Tom and Bill are both French. 汤姆和贝尔他们两个人都是法国人。
2. The blind man used both of his arms to touch the elephant. 那个盲人用他的两只手去触摸大象。
3. Jerry, Bill, and Tom, they all speak Chinese. 杰瑞、贝尔、汤姆，他们三个人都说中文。
4. All of my classmates went to the airport yesterday. 我班上的同学昨天全都去了机场。

观察上面的例句，能不能发现以下规律？

both 是“(两者)都”， 而 all 是“(三者或三者以上)都”