I found this sentence from a Shinkansenmaster reading textbook.

> 基本語彙の語源は本当は問うてはいけないのかもしれない。

But てform of 問う is 問って right?

Please explain why it is used in such way. Thank you.
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2018-07-21T14:33:59.013
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2018-07-21T14:46:44.997
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question
grammar
問うてはいけない？why not 問ってはいけない