being on the train but not in order to use it

[Jaro7788]

I'm aware that we are supposed to be on the train and the definite article here is needed whether we mean a particular train or not. That is the rule we are all familiar with. However, suppose we enter a train but we do not expect it to move anytime soon. Or even worse - the train is badly damaged. Now, in order to define our location, are we still going to say "I'm on the train" or perhaps this is the time for dropping the definite article? Mind you: the person we are talking to (via cellphone) has no idea we were intending to visit any damaged train.

[Dozy]

In that case you would say "I'm on a train". However, "I'm on a train" is possible even if the train is in normal operation. It has more of a sense that the other person doesn't really care which train it is. For example, if you were going to visit someone, and they rang you to check on your progress, you would say "I'm on the train". If they rang you about some other matter and had no particular interest in your journey, then you could say "I'm on a train".

[Jaro7788]

There you got me surprised... I haven't been sure of the situations like the one mentioned above but as far as travelling by train was concerned, I've been like 100% certain that "on the train" is a must. So, according to you, is it the same as with buses? You know, normally "on a bus" but "on the bus" when the bus is specific.

[Mister Micawber]

When they are our regular or expected modes of transportation, native speakers use 'on the train/bus'. The indefinite article is also fine, but I think you will mostly hear it when that mode or it is unexpected in some way.

'On bus/train' is not possible in any context. Do not confuse it with the idiomatic mode of transportation 'by bus/train/etc'.
_________________
Native English teacher at Mister Micawber's