What is the difference between に違いない and きっと～でしょう?


Do に違いない and きっと～でしょう have the same meaning and usage? I learned that に違いない is
based on feeling of the speaker, but I couldn't find what きっと～でしょう is based
on. So I'm wondering if きっと～でしょう is based on logic or feeling just like に違いない?




I see two differences. Basically きっと is even more subjective.

  * きっと is typically used to describe a _desirable_ outcome. きっと失敗するだろう is grammatical but this can sound you are hoping someone will fail. 失敗するに違いない is neutral in this regard.
  * きっと tends to be used when you say something based on your subjective/personal expectation rather than an objective estimation. Saying きっとうまくいくよ ("It's gonna be fine") to encourage someone is usually safe even when the objective chance of success is 50%. Saying うまくいくに違いない in a situation like this can sound irresponsible.

