Comment by thaumasiotes

> Inter + ferire = to strike one another. Makes sense.

I guess, but I don't really think of interfering as a mutual thing. I see interfere more like intervene or interpose, where the subject of the verb inserts himself between two other things. (As, in the example above, "my" neighbor places himself into the middle of the relationship between me and my television.)

If I'm interfering with you, it is not necessarily the case that you are also interfering with me. And it certainly couldn't be said that "we are interfering [end of sentence]" in the same way that it could be said "we are fighting".

The use of with to mark an indirect object does tend to suggest that the sense of the verb was more mutual at an earlier point, though.