When learning じゃない and ではない, we briefly mentioned that these constructions are regularly partnered with the particle か, in order to form a (usually casual) question. In this lesson, we will further explore this usage.
Unlike じゃない and ではない (which need to come after a noun or な-Adjective), じゃないか is able to to be attached to the end of almost any phrase, to indicate a question. This is very similar to finishing a sentence with ‘isn’t it?’ in English.

• キヨコはもうすぐ来（く）るんじゃないか。
  Isn't Kiyoko coming soon?
• そのカメラは高（たか）いじゃないか。
  That camera is expensive, isn't it?
• この着物（きもの）は綺麗（きれい）じゃないか。
  This kimono is beautiful, isn't it?
• あなたの車（くるま）は私（わたし）の車（くるま）より速（はや）いじゃないか。
  Your car is faster than my car, isn't it?

When じゃないか is too casual, ではないか will be used instead. Despite being more formal, this may sound a bit stiff at times, so is best only used when politeness is expected.

• これは台風（たいふう）の影響（えいきょう）ではないか。
  This is the typhoon’s effect, isn't it?
• 遊（あそ）んでないで明日（あした）のテストの勉強（べんきょう）をした方（ほう）がいいんではないか。
  Without mucking around, wouldn't it be better if you studied for the test tomorrow?