Why is は appropriate for てはいけない?


Why does てはいけない use は? I know it's a construction, but where did it come from?
て form verbs are not nouns, it doesn't make sense to me that は could be used
with them.




THe は in ～てはいけない. Is actually not the topic marking particle, but a different
particle entirely. IT's kind of like how the particle に has a number of
different uses. In this case the は is used to emphasize the negative part of
the sentence. You'll see in other places が being replaced by は before ない or
another negative verb or adjective.

Edit: I found some more information on the subject. [This
website](http://www.learn-japanese-adventure.com/japanese-particles-
change.html) does a good job discussing this concept as I understand it.

