Learn Hardcore Korean: bame iljjik jayo, geuraeseo da-eum nal pigonhaji anhayo. - I go to sleep early at night, so I'm not tired the next day.

In Korean, the particle -에 attaches to time nouns to mean “at” or “on.” Since 밤 means “night,” 밤에 literally means “at night.” You’ll also see -에 used with words like 아침에 (in the morning), 점심에 (at noon), and 월요일에 (on Monday).

What does 일찍 mean, and why is it placed before 자요?

일찍 is an adverb meaning “early.” In Korean sentence order, adverbs describing manner (how) typically come right before the verb they modify. So 일찍 자요 means “go to sleep early.”

Why is the verb 자요 instead of 자다?

자다 is the dictionary (infinitive) form “to sleep.” When you make a polite present-tense statement, you change 자다 to 자 + -아요 → 자요. The -아요/어요 ending is the standard polite speech level.

Where is the subject in this sentence? Why isn’t there something like 저는?

Korean often omits subjects when they’re clear from context. Here, it’s understood that you (or “I”) are the one sleeping early. You could say 저는 밤에 일찍 자요 for emphasis or clarity, but dropping 저는 is perfectly natural.

What role does 그래서 play, and can I start a sentence with it?

그래서 means “so” or “therefore” and links a cause to its result. In this sentence, it connects “I sleep early” to “I’m not tired.” In Korean, it’s completely fine to start a clause or sentence with 그래서, especially in spoken or informal contexts.

Why is 다음 날 written as two words, and what does it mean?

다음 means “next,” and 날 means “day,” so 다음 날 = “the next day.” Standard Korean writing treats time noun compounds like this as two words. In casual contexts you might see 다음날 without a space, but the separated form is more textbook-style.

How is the negative 피곤하지 않아요 formed, and could I say 안 피곤해요 instead?

피곤하다 is an adjective meaning “to be tired.” To negate it, you can attach -지 않다 to the stem: 피곤하 + 지 않다 → 피곤하지 않다, then apply the polite ending -아요 → 피곤하지 않아요. Alternatively, Korean allows 안 + adjective, so 안 피곤해요 is also correct and more casual.

Could I switch the order to 일찍 밤에 자요?

While Korean word order is flexible, the natural sequence is time → manner → place → verb. So 밤에 (time) 일찍 (manner) 자요 (verb) sounds most idiomatic. Putting 일찍 before 밤에 isn’t strictly wrong, but it can feel awkward or imply a different emphasis.

Is the comma before 그래서 necessary?

The comma here is stylistic, showing a pause or linking two clauses. You could also split it into two sentences:
“밤에 일찍 자요. 그래서 다음 날 피곤하지 않아요.”
Either way is acceptable; the comma simply highlights the connection.