文章译自 Why do we say "on the bus" or "on the train" but "in the car"?，作者 Chris Aubeck。
译者注: 在学习英语的过程中，我总是会遇到以下情况：当我初次碰到某个陌生的词时，我总会在接下来几天内多次碰到该词。 重复的相遇又加深了我对该词的记忆，久而久之，我记的单词也越来越多。
本文是在我和微信群里的同事讨论为什么有些交通工具用 on 而另一些交通工具用 in 之后，Quora订阅推送给我的文章，是不是巧合？
The general rule:
For vehicles, anything considered to have a large floor space is ON and a small floor space is IN. Large means you can or must walk there (you walk to your seat, to the toilet, etc.), small means you can’t comfortably walk there (you either just stand or sit).
对于交通工具来说，凡是被认为地板面积大的就是 ON，地板面积小的就是 IN。
In English we distinguish between platforms and containers.
In the topic of vehicles:
For walled vehicles, large floor spaces are considered platforms, small floors are considered containers.
Therefore it's in a car, in a small boat, in a helicopter, in a rocket, in a hot air balloon, in a small plane (think of an old biplane). A lift would be in.
But we say on a train, on a ship, on the space shuttle, on a passenger plane, etc.
When the vehicle has no walls (i.e. it is not an enclosure) it's a platform so we say on, too. Therefore, it's on a skateboard, on ice skates (platforms for your feet). On a horse, on a bike (platforms for your bottom).
因此有 in a car、in a small boat、in a helicopter、in a rocket、in a hot air balloon、in a small plane（想想老式双翼飞机，an old biplane）。在电梯里也是用 in。
但其它的情况，我们会说 on a train、on a ship、on the space shuttle、on a passenger plane 等等。
当车辆没有围墙时，它就是一个平台，所以我们说 on。因此，on a skateboard、on ice skates(platforms for your feet)。On a horse、on a bike(platforms for your bottom)。
Platforms needn’t be large, they just need to be platforms instead of containers. Think:
On a stage, on a table. Our feet are like platforms for our bodies, and we say to travel on foot. You can put your foot in a shoe (container). We like to regard clothes in general as containers (in a suit, lady in red, etc.).
On a stage，on a table。我们的脚就像我们身体的平台，我们说要徒步旅行(travel on foot)。你可以把脚放在鞋子（容器）里(in a shoe)。我们通常把衣服视为容器（穿西装 in a suit、穿红衣的女士 lady in red 等）。
Interesting fact: for objects, a platform with one or two walls is still a platform (on). But with three walls, we usually say it’s a container (in). That’s why a stackable plastic office tray has three walls and is a container (think: inbox) and we sit in an armchair. Note that sofas, perhaps because many originally didn’t have arms, are mostly considered platforms (on). It could also just be to contrast with the single-seated armchairs.
Because the language is dynamic, and because it is old, some exceptions will emerge but this is the basic rule. If you stick to the general rule you'll rarely be wrong. Once you begin to visualize surfaces as platforms, on becomes logical too for other kinds of things: on a screen, on paper, on a page. If you’re teaching English, think about walls, ceilings and floors!
In a car, on the car roof.
In a book, on a page. A book is a container of pages.
In a car, on the car roof. (在车内，在车顶)
In a book, on a page. A book is a container of pages. (在书里，在某一页。书是页面的容器。)
Edit: When I wrote this I had no idea people would find it useful, so thanks for your comments both private and otherwise. The above is not a full explanation, there is more. When we consider transport we should focus on this idea: on = surface, and therefore on = board/platform. If the transport is considered predominantly a container rather than a platform, expect to find “in” (a typical elevator, for example).
更新： 我写这篇文章的时候没想过大家会觉得有用，所以感谢大家私下和其他场合的评论。以上不是完整的解释，还有更多。当我们考虑运输的时候，我们应该关注这个概念：on = 表面，因此 on = 板/平台。如果运输主要考虑的是容器而不是平台，通常会看到 "in"（比如典型的，电梯）。
There are alternative explanations online, which unfortunately aren’t very complete or are simply strange, but over the 27 years I've been teaching I've found the information here to be what gives English language learners that Eureka! moment. I don’t delve into the etymology of “on” and “in” because language students don't find it useful.
网上有其他的解释，遗憾的是，这些解释不是很完整，或者根本就是奇怪的。但在我27年的教学生涯中，我发现这里的信息可以让英语学习者有恍然大悟的感觉。我不会深究 "on "和 "in "的词源，因为语言学习者不会觉得它有用。
There are interesting exceptions to the “surface” rule but nothing too complicated. The palm of your hand is considered to be a container (in). The back of your hand a surface (on). Dirt or stains on the skin are always on. It’s not illogical.
"surface" 规则有一些有趣的例外，但没有什么太复杂的东西。你的手掌(palm)被认为是一个容器(in)。手背(back of your hand)是一个表面("on")。皮肤上的灰尘或污渍总是on。这并非不合逻辑。
In class I also teach on = contact. This is true in all physical cases (I write cONtact on the board).
在课堂上，我也这样教: on = contact(接触)。在所有的物质情况下都是如此 (I write cONtact on the board)。
I could also go into the extended use of ON and IN for electric devices and non-physical cases but the question hasn't come up.
Why do we say "on the bus" or "on the train" but "in the car"?: https://qr.ae/pNYuT5