Learn Hardcore Korean: oneul sueobi neomu jiruhaeyo.

오늘 means “today.” In Korean, time expressions (like 오늘, 어제 “yesterday,” 내일 “tomorrow”) typically come early in the sentence to set the temporal context. The usual order is Time – Subject – (Object) – Verb/Adjective, so putting 오늘 first tells the listener when you’re talking about.

Why is there -이 after 수업, and what’s the difference from using -은/는?

-이/가 is the subject marker, indicating that 수업 (class) is the grammatical subject of the sentence. You could also say 오늘 수업은 너무 지루해요, using -은/는 (the topic marker). The nuance changes slightly:

수업이 너무 지루해요 simply states “The class is boring.”
수업은 너무 지루해요 implies “As for the class (in contrast to something else), it’s boring.”

Both are correct, but -이/가 is more neutral when just describing the subject.

What does 너무 mean here, and does it always have a negative “too” sense?

By default, 너무 means “too” (i.e. excessively). So 너무 지루해요 literally means “(It’s) too boring.” In everyday casual speech, however, Koreans often use 너무 like “very”, even in positive contexts (e.g. 너무 맛있어요 “It’s very delicious”). Just be aware that in more formal writing or speech, 너무 can still carry that “excess” nuance.

What part of speech is 지루해요, and how is it formed from 지루하다?

지루하다 is a descriptive verb (형용사) meaning “to be boring.” In Korean, adjectives conjugate exactly like action verbs. To make the polite present tense:

Drop -다 from 지루하다 → 지루하
Add -아요/-어요 (here 아 matches the vowel 하) → 지루하 + 아요
Contract 하 + 아 to 해 → 지루해요

So 지루해요 is simply the polite form of “is boring.”

Why is 지루해요 at the end? How does this word order compare to English?

Korean follows a Subject–Object–Verb/Adjective (SOV) order, and adjectives (descriptive verbs) come at the end as predicates. In your sentence:

Time: 오늘
Subject: 수업이
Adverb: 너무
Predicate: 지루해요

In English we’d say “Today the class is too boring,” with the verb in the middle (SVO). Korean always reserves the final position for the verb or adjective.

Why is there no subject pronoun like 저 (“I”), and can I include it?

Korean often omits pronouns when the context makes them clear. Here, it’s obvious you’re talking about your own feeling. If you want to be explicit, you can add the topic marker -는:

저는 오늘 수업이 너무 지루해요.
(As for me, today’s class is too boring.)

It’s perfectly grammatical, though often unnecessary in casual conversation.

What level of politeness is the -요 ending in 지루해요, and how can I adjust the formality?

The -요 ending is the polite informal style (해요체), suitable for strangers or acquaintances. To change levels:

More formal (합니다체): 지루합니다.
Less formal/casual (반말): 지루해.

Choose your ending based on who you’re speaking to and the setting.