Learn Hardcore Korean: seonsaengnimi dasi seolmyeonghae jusyeoseo ije ihaehaesseoyo. - Now I understand because the teacher explained it again.

-이/가 marks the grammatical subject. Here, the teacher is the subject of the reason clause: “because the teacher explained again.” In a subordinate reason clause like this, a subject marker (이/가) is the default. 은/는 is a topic/contrast marker; using 선생님은 would imply contrast (e.g., “As for the teacher (as opposed to others)…”), which isn’t needed here. If you want a more honorific subject marker, you can use 선생님께서.

Why is it 설명해 주셔서 and not just 설명해서?

-아/어 주다 is a benefactive auxiliary meaning “do something for someone.” 설명해 주셔서 conveys that the teacher explained for the speaker’s benefit, which sounds appreciative. Without 주다 (설명해서), it simply states that the teacher explained, with no “for me” nuance.

What exactly is inside 주셔서?

Breakdown:

주다 “to give” used as benefactive auxiliary “do for (me)”
Honorific: 주시다 (to honor the subject, the teacher)
Reason connective: -어서
Phonetic contraction: 주시어서 → 주셔서 So 설명해 주셔서 = “because (the teacher) kindly explained (for me).”

Is 주셔서 past tense? The explaining happened before understanding.

No. Tense is not marked in the -아서/어서 clause. You do not put past before -아서/어서 (forms like “줬어서” are nonstandard). The past is shown in the main clause (이해했어요). If you need to make the cause explicitly past, use forms like 주셨기 때문에 or 주신 덕분에.

Can I say 설명해 줘서 instead of 설명해 주셔서?

Only if the subject is someone you don’t honor (e.g., a friend). With a teacher as subject, keep the honorific: 주셔서. Using 줘서 about a teacher sounds impolite.

Why is “I” missing? Who understood?

Korean drops obvious subjects. The main predicate 이해했어요 is first-person in context, so “I” is understood without saying 제가.

Why past tense in 이해했어요 instead of present 이해해요?

Korean often uses past to express the moment of realization: “I got it (now).” 이제 이해했어요 means “Now I’ve understood.” Present 이해해요 is more “I understand (now/in general)” without highlighting the moment it clicked.

What’s the difference between 이제 and 지금 here?

이제 marks a change point: “from now (as a result) / at last.” It implies contrast with the past (previously didn’t understand).
지금 is “right now (time).” 이제 이해했어요 is more natural because it emphasizes the change from not understanding to understanding.

Can I use -니까 or -기 때문에 instead of -아서/어서?

Yes, with nuance differences:

-아서/어서: neutral, background reason, often cause-effect.
-니까: more assertive/subjective reasoning; commonly used before requests/commands.
-기 때문에: explicit, sometimes stronger/clearer cause. All three are fine here: …주셔서/주셨으니까/주셨기 때문에 이제 이해했어요.

What does 다시 modify, and can it move?

다시 means “again” (repeat). It modifies the explaining. Typical placements:

선생님이 다시 설명해 주셔서…
선생님이 설명을 다시 해 주셔서… Both are natural; the second slightly emphasizes the act of explanation itself being repeated.

Is there a difference between 다시 and 또?

다시: repetition of the same action (again).
또: “again/also” in the sense of an additional occurrence; can sound like “in addition.” Here, 다시 is the safest choice for “explain again.” 또 설명해 주셔서 can imply “explained yet another time.”

Could I drop 주다 and say 설명하셔서?

Yes: 선생님이 다시 설명하셔서… is grammatical and polite (honorific -시-). But it lacks the benefactive “for me” nuance that 설명해 주셔서 carries, which suits this appreciative context.

Is the spacing 설명해 주셔서 or 설명해주셔서?

Standard spacing writes auxiliary 주다 separately: 설명해 주셔서. Writing it together (설명해주셔서) is very common informally but not the recommended standard.

Can I use 선생님께서 instead of 선생님이?

Yes. -께서 is the honorific subject particle and sounds more respectful/formal: 선생님께서 다시 설명해 주셔서….

Why is honorific -시- only in the first clause?

Honorific -시- honors the subject of that verb (the teacher in 주셔서). You don’t honor yourself, so 이해했어요 has no -시-.

Can I say 이제 이해가 됐어요 or 이해가 가요?

이해가 됐어요 (passive “became understood”) is very natural: “It made sense to me.”
이해가 가요 is colloquial and common, roughly “I get it.” The past version 이해가 갔어요 is also used conversationally. The most neutral choices here are 이해했어요 or 이해가 됐어요.

Can I say 선생님은 다시 설명해 주셔서…?

Only if you want a contrastive/topic nuance (e.g., “As for the teacher, because he explained again…” implying contrast with someone else). Otherwise, stick with 선생님이/께서.

Can I leave out 이제, or add 덕분에?

Omitting 이제: …주셔서 이해했어요 just states you understood, without highlighting the change.
Adding 덕분에 (thanks to): 선생님이 다시 설명해 주신 덕분에 이제 이해했어요 explicitly shows gratitude.

Is a comma after 주셔서 required?

Optional. You can write either way:

선생님이 다시 설명해 주셔서, 이제 이해했어요.
선생님이 다시 설명해 주셔서 이제 이해했어요. Both are fine in modern Korean punctuation.