で　している　ｖｓ　をしている
 

私は森の中で走っている
私は森の中を走っている

I understand で but I cant really tell the difference if you use を
I just learned this sentence structure.


I asked my Japanese boyfriend, he said kinda the same. I said to him does it mean that one is just saying doing something in the forest and the other one means like, running through the forest, like they are running "the" forest.
and he said yea kinda, but you can say both.


I wanna get feed back from you guys, cause you explain stuff very well. and my boyfriends not good at telling the difference between things to me.

Well, で is a particle, which can among others indicate the location of an action. You can also use the を to mark the place where a person is on move, like "I´m running through the forest" or "I´m walking in the park" or "I cross a crossroad" ...

I will take a crack even though I may just be another Japanese dude like your BF.

It is true that both are 100% grammatical but the first one would not be said by too many native speakers. To be strict, the two DO NOT mean the same thing or at least they will not be used in the same situations.

森の中で走っている sounds like you are an athlete and the forest happens to be your favorite place for the running part of your practice/excercise. Someone asks you where you do your running and you may answer by saying this. One does not have to be an athlete but the phrase does have a slight implication that one has selected the forest as a place to run.

森の中を走っている sounds more normal/natural. You either selected the forest to run or you simply wandered into a forest while running. This phrase serves more purposes than the other. It can be used in both prose and poetry while the other cannot. The other one sounds way more business-like.
This one is almost, if not always, saying that you have found yourself running through the forest.