What it means
にかたくない expresses that something can readily be imagined, inferred, or understood. It is a formal, restrained way to say that an action or conclusion is not difficult to carry out mentally, rather than a general statement that a practical task is easy. The construction is especially common with nouns such as 想像, 理解, and 推察.
Usage note
にかたくない is strongly formal and is most natural in written or ceremonious contexts. It usually follows an abstract noun referring to a mental activity, so everyday speech generally uses a more direct expression such as 想像しやすい or 想像できる instead.
How to use it
Nounにかたくありません
私たちの驚きは想像にかたくありません。
Our surprise is not difficult to imagine.
Nounにかたくない
私たちの驚きは想像にかたくない。
Our surprise is not difficult to imagine.