いて use as a reason or something else


> 昨日は疲れていてテスト勉強ができませんでしたが、今日はできると思います。

In this sentence, is this `いて` after `疲れて` explaining the reason? Why was he
not able to study? Why can't we use `から` or `ので`?




You could use ので or から, you just don't have to as it can be implied. Compare
«I was tired yesterday and I couldn't study» vs «Because I was tired yesterday
I couldn't study». Your example is essentially the former.

The いて is the te-form of いる which marks the verb as progressive or ongoing.

疲れる — To be tired

疲れている — Is tired

疲れていて — te-form of being tired

