にわかに vs. いきなり: What's the difference?

Both can express sudden meaning, but there are slight differences in usage.

にわかに

It means sudden, but there is no specific restriction on the process before and after the change or action. It implies that the previous process ends and suddenly turns into another process.

For example, when we went out to play on the weekend, the weather was fine and it was almost sunny all day, but it suddenly rained in the evening. The sunny state ended relatively completely and suddenly turned into a rainy state.

いきなり

It also means sudden, but there are specific constraints on the process before and after the change or action. It implies that the previous process has not ended, or without any warning, it suddenly turns to the following process.

For example, we were discussing work, but before the discussion was finished, the boss suddenly became angry; that is, the discussion process was not over, and the boss ended it with an angry process. Here, we use いきなり.

In addition, いきなり is used much more frequently than にわかに in daily conversation because there are many situations to express the change of things without warning.