Learn Hardcore Korean: chaegi neomu dukkeowoyo.

이 is the subject particle that marks 책 as the subject of the sentence. Korean uses 이/가 to indicate what the statement is about: 이 follows nouns ending in a consonant, while 가 follows those ending in a vowel.

What does 너무 mean and how is it used here?

너무 generally means too or so/very, depending on context. It intensifies the adjective that follows. In 책이 너무 두꺼워요, it carries the sense of too (excessively), implying the book’s thickness is a problem.

Why is 두껍다 conjugated as 두꺼워요?

Adjectives in Korean are treated as descriptive verbs. To form the polite present tense:
• Drop -다 from 두껍다 → 두껍
• Add -어요 → 두껍어요
• Sound assimilation simplifies 두껍어요 to 두꺼워요.

What level of politeness does the ending -요 indicate?

The -요 ending marks the polite informal style (아/어요체), suitable for everyday conversations with people who are not extremely close or vastly older. It’s the default polite register.

Can 너무 ever mean very without a negative connotation?