Difference between よもや and まさか?


They seem interchangeable when used in the meaning of conveying disbelief of
something.

> **まさか** この時点でやめる気じゃないよね？  
>  **よもや** この時点でやめる気じゃないよね？




When まさか and よもや are used as [negative polarity
items](https://japanese.stackexchange.com/a/16060/5010), they are basically
interchangeable, but よもや is more literary and less common. In casual speech,
まさか is normally used. A negation like ないだろう, あるまい, 思わなかった or 訳がない will follow,
but this part is often omitted.

  * {まさか/よもや}彼女が女王ではないだろう。
  * {まさか/よもや}君がいるとは(思わなかった)。
  * 彼も{まさか/よもや}そんなことは言わないでしょう。

まさか is also often used like an interjection, but よもや is almost never used like
this. We say "まさかー(笑)" ("No way! LoL") but never "よもやー(笑)". As an
interjection, まさか means "Could it be...!? / By any chance ...!?" or "It
couldn't be! / No way!" depending on the context and the intonation.

  * まさか、殺したのは俺なのか…？  
Could it be... _me_ who killed him?

