modality N1 rare writtenliterary
を禁じ得ない — cannot help (feeling)
を禁じ得ない ・ をきんじえない
A full written guide for を禁じ得ない is on the way.
This point is mapped in the grammar tree, but its examples, formation table and usage notes haven't been written yet. The fastest way to learn it now is to meet it in real sentences inside Jengo.
See を禁じ得ない in real sentences
Jengo shows を禁じ得ない the way you actually meet it: inside real Japanese sentences, so it sticks instead of staying an abstract rule.
Study it in JengoSources Compiled with reference to A Dictionary of Advanced Japanese Grammar. Editorial confidence: low.