At least twice in recent days, I’ve seen people using “in dem” and “indem” incorrectly (I think one each of the two possible directions of mix-up).

It should be simple, really: the two-word one is the more literal “in which”; the one-word one is the fossilised “by” indicating the means:

“Er öffnete den Kofferraum, in dem er das Schloss ( Read more... )