What does "に" mean in "精神的に疲れたので早く寝ます"?


Context: 精神的 **に** 疲れたので早く寝ます。

Is "に" a preposition here?

If "精神的" is a adjective, is it telling that need to use a preposition between
a adjective(精神的) and a verb(疲れた)?




By itself [精神的](https://jisho.org/word/%E7%B2%BE%E7%A5%9E%E7%9A%84) is a な
adjective. But in your example above it essentially becomes an adverb when
paired with the に. In English this can be seen as adding on the 'ly' suffix to
a word.

So we get something like mentally, spiritually, emotionally, or etc depending
on the context for 精神的. Overall giving us something like:

> 精神的に疲れたので早く寝ます
>
> Since I'm mentally worn out, I'm going to bed early.




By itself [精神的](https://jisho.org/word/%E7%B2%BE%E7%A5%9E%E7%9A%84) is a な
adjective. But in your example above it essentially becomes an adverb when
paired with the に. In English this can be seen as adding on the 'ly' suffix to
a word.

So we get something like mentally, spiritually, emotionally, or etc depending
on the context for 精神的. Overall giving us something like:

> 精神的に疲れたので早く寝ます
>
> Since I'm mentally worn out, I'm going to bed early.

