Prepositions are tricky in all languages, because they usually don’t have any rules that a student can memorize and use every time without exception.
Why, for example, do we say we are fond of but in love with someone? Why are we happy about something, but delighted with the same thing? It can certainly be very frustrating for a student when there doesn’t seem to be any logic or consistency to the new language.
When we talk about ways to travel, however, there are a few rules that work 100% of the time. Let’s take a look at them:
General Ways to Travel
When talking about general ways to travel, we always use the preposition “by.” We can travel by bike, by motorcycle, by car, by van, by lorry, by truck, by train, by plane, by bus, by ship, by tram, or by boat.
We can also use by to refer to the transportation environment (by sea, by land, by air) or the surface area (by rail, by road, by water).
Specific Transport Vehicles
When we talk about specific transport vehicles, however, we need to switch to either in or on. How do we know which to use? Easy, if you remember this simple rule: If you must sit inside the vehicle, we use in.
Some examples would be: "in a car", "in a truck", or "in a helicopter": it is almost impossible to stand in them.
If you can stand or walk on the vehicle, then we use on. So we go on a ship but in a rowboat; we go on a bus but in a taxi. Other examples of when we use on would be on a plane, on a tram, on a ferry, on a subway, or on a train — again, you can stand or walk on all of these, even when they are in motion. Finally, if we actually sit or stand upon the top of the vehicle, then we also are on it. So we go on a bicycle, on a surfboard, on a motorcycle, on a skateboard, on skis, on ice skates, on a snowboard, etc.
Keep in mind that the preposition in is different from the short form of inside. So, you can be inside an airplane or a cruise ship, but that doesn’t mean we use the preposition in (we can stand and walk on both a plane and ship, so we use on as our preposition).
ON and BY
And, where does that leave the most basic form of transportation — walking? Well, the same rules apply: we go by foot (meaning as a general way of moving from one place to another) or we go on foot (meaning we are on top of our feet!). Therefore, both are correct ways to describe walking.
The key thing is to recognize when something is general and when something is specific. A person can travel by bus across England, and then say that on the bus from London to Manchester he met a very nice girl. Here, he is talking about a specific bus he rode on (the one from City A to City B, or the one that leaves at 11:20, etc.) not the form of travel (by bus).
And luckily, there are a lot of popular songs that use these prepositions correctly: “Leaving on a Jet Plane,” “[On that] Midnight Train to Georgia,” “On a Slow Boat to China” and “In Cars,” to name just a few.
To hear this explained in a bit more detail and to see an exercise that will test your understanding of these prepositions, you can go to a YouTube video I’ve created: