True, the words but, concerning, considering do function in some sentences differently from prepositions.

I don't have a lot of time* and won't till probably Thursday, but I'll just say that, maybe you can shoehorn those words into the preposition cubbyhole but it's not something I'd do to poor, impressionable, young schoolkids.

*I haven't even had a chance to get caught up on this thread, so I apologize to any chopped liver I've left scattered about.

Addendum: I am reminded that a quick scan has indicated that there are a whole lot of posts in this thread that I won't have to read, so my catching up may not take so long.