What is the difference between "trans" and "tra"?

Question

These are some examples. Could you explain them, and mark the invalid ones?

• Mi iras tra la strato.
• Mi iras tra la straton.
• Mi iras trans la strato.
• Mi iras trans la straton.

Answer 1

I'd like to change the examples slightly to this, so not by strato, but by parko.

Mi iras tra la parko. (I am going through the park.)

Usually you don't use the direction marker -n here, but it's not completely forbidden. You could use it for example to emphasize that you are going straightly through the park and straightly aiming the exit at the other side in order to proceed. But if you follow the rule "No -n after tra" you are always ok.

Mi iras trans la parko. (I am walking around at the other side of the park)

The preposition trans without accusative of direction "-n" indicates a place. So no direction indicated.

Mi iras trans la parkon. (I am going to the other side of the park.)

Here we have the accusative of direction after trans, so we indicate a direction. We don't know however, if it's through the park, around the park or through an underground tunnel.

Answer 2

Trans means "on the other side of".

If you're on one side of the street and then you iras trans la straton - you will then be trans la strato (on the other side of the street.)

(Trans la strato describes a location on the other side. Adding the -n (trans la straton) means there is motion toward that location.

In contrast

Tra includes the idea of passing through the inside of something.

The phrase mi iras tra la strato implies that we're thinking of the street as a place of activity with buildings on either side, perhaps with kiosks and apple carts here and there, and not just as a surface. We're inside of this space and are traveling around in it.

Finally - tra la straton/stratojn is not a phrase that I recall ever spontaneously using, and initially I could not find any examples of it in use. Given the definition of tra in PIV as indicating motion (not location), the object would not normally take an -n. PMEG says it can take an -n but rarely needs to. PIV includes some examples of it with an -n, but at least the 1970 version of PIV includes a note saying that Zamenhof advised against it.

Answer 3

Prepositions can be rather tricky. I understand you find these confusing since they look so similar. Their meaning though, is very different:

tra - through

trans - across

A teacher of mine used a very good example, where both "tra" and "trans" are suitable:

Mi iras tra la koridoro. (I am going through the corridor, from one end to another.)

Mi iras trans la koridoro. (I am crossing the corridor. Imagine opening a door, crossing the corridor, and then entering a door on the opposite wall of the first one).

I've seen trans la strato and trans la rivero. But it is not common to use "tra" with these. (unless you imagine a street as something one can be inside of, or is talking about swimming through a river) Instead there is laŭ la strato/rivero (laŭ - along), and en la strato/rivero.

Since some prepositions themselves imply direction one does not use the accusative n-ending with them. "Tra" is one of these. On the other hand, it is not clear whether or not trans implies direction. I've learned that it does, while PMEG says the opposite.