想像に難くない — is 難くない doing something weird to 難い here?

Question

「Noun/Verb + に難くない」apparently means 'not difficult to ~', e.g. 「彼の怒りは想像に難くない」= 'it's not hard to imagine his anger.' But 難い attached directly to a verb stem (想像し難い) already exists separately. Is 「に難くない」just the negated version working through a noun, or is there a subtle difference in what kind of predicates it accepts?

Accepted Answer

這個文型幾乎只跟固定幾個漢語動詞名詞搭配——想像、理解、察する——變成「想像に難くない」「理解に難くない」這種半慣用語，不是自由生產的文法（不會說「食べるに難くない」）。跟直接接動詞ます形的「〜難い」比，範圍窄很多但更書面、更常在新聞評論用。