Present, Future 思いがけない is [x] 思いがけなくない is not [x] Past 思いがけなかった was [x] 思いがけなくなかった was not [x] Te-form, Continuative 思いがけなくて is [x] and... 思いがけなくなくて is not [x] and... Provisional 思いがけなければ if it is [x] 思いがけなくなければ if it is not [x] Conditional 思いがけなかったら when/if it is [x] 思いがけなくなかったら when/if it is not [x] Adverbial 思いがけなく [x]-ly Noun form 思いがけなさ [x]-ness