The suffix -을 is an object marker that is attached to nouns ending in a consonant to indicate that they are the direct object of a verb. It functions similarly to -를, which is used when the noun ends in a vowel.

Usage of -을:  NC-을

Marking the Direct Object of a Verb
-을 is attached to nouns that end in a consonant.
If the noun ends in a vowel, -를 is used instead.

Example:
책을 읽다 → “To read a book” (책 ends in a consonant, so -을 is used.)
영화를 보다 → “To watch a movie” (영화 ends in a vowel, so -를 is used.)

Emphasizing the Object of an Action
-을 helps clarify what is being acted upon in a sentence.

Example:
나는 밥을 먹었어요. → “I ate rice.” (Emphasizes that rice was eaten.)
그는 문제를 해결했다. → “He solved the problem.”

Comparison with Topic and Subject Markers
Unlike -은 / -는 (topic markers) and -이 / -가 (subject markers), -을 / -를 specifically marks the object of an action.

Example:
나는 책을 읽어요. → “I read a book.” (책을 → direct object)
책이 재미있어요. → “The book is interesting.” (책이 → subject)

Summary:
-을 is the direct object marker used when a noun ends in a consonant.
-를 is used when the noun ends in a vowel.
It helps indicate what an action is being performed on.
Common examples: 책을 읽다 (“to read a book”), 문제를 해결하다 (“to solve a problem”).

The suffix -의 is a possessive marker that is used to indicate ownership, relationship, or association between two nouns.
It functions similarly to the English apostrophe ‘s or the word “of” in phrases like “John’s book” or “the color of the sky.”

Usage of -의:

Expressing Possession (Belonging)
-의 is placed between two nouns to show that the first noun owns or is related to the second noun.

Example:
나의 책 → “My book” (나 = “I” → 나의 = “mine”)
선생님의 연필 → “The teacher’s pencil” (선생님 = “teacher” → 선생님의 = “teacher’s”)

Indicating Relationships
-의 can indicate associations between things, such as kinship, attributes, or concepts.

Example:
아버지의 친구 → “Father’s friend” (아버지 = “father”)
서울의 날씨 → “Seoul’s weather” (서울 = “Seoul”)

Describing Attributes (Adjectival Use)
-의 helps describe qualities, often similar to “of” in English.

Example:
하늘의 색 → “The color of the sky” (하늘 = “sky”)
생명의 의미 → “The meaning of life” (생명 = “life”)

Spoken vs. Written Korean (Omission in Speech)
In spoken Korean, -의 is often dropped in casual conversation, but in written Korean, it remains more formal.

Example:
Instead of “나의 책”, Koreans often say “내 책” (“My book”) in daily conversation.

Summary
-의 is the possessive marker in Korean, similar to ‘s in English.
It shows ownership, relationships, or attributes.

In spoken Korean, it is often omitted for simplicity.

Examples:
나의 가족 (“My family”)
학교의 이름 (“The name of the school”)
친구의 집 (“Friend’s house”).

-이 is the subject marker used when a noun ends in a consonant.
It indicates who or what is performing an action.
It helps emphasize the subject of the sentence.

-이 is used with consonant-ending nouns (e.g., 사람이, 책이).
-가 is used with vowel-ending nouns (e.g., 고양이가, 학교가).

The suffix -이 is a subject marker that is attached to nouns ending in a consonant to indicate that they are the subject of a sentence. It works in the same way as -가, which is used for nouns ending in a vowel.

Usage of -이:   NC-이

Marking the Subject of a Sentence
-이 is attached to nouns that end in a consonant to show that they are performing the action or being described.

If a noun ends in a vowel, -가 is used instead.

Examples:
학교 (“school”) → 학교가 크다. (“The school is big.”) → Ends in a vowel, so -가 is used.
사람 (“person”) → 사람이 왔다. (“The person came.”) → Ends in a consonant, so -이 is used.

Emphasizing the Subject
-이 helps clarify who or what is performing an action, especially when making a distinction.

Example:
책이 떨어졌다. → “The book fell.” (Emphasizes that the book fell, not something else.)
고양이가 뛰어다닌다. → “The cat is running around.”

Comparison with Topic Markers (-은 / -는)
While -이 (or -가) specifically marks the subject, the topic markers -은 / -는 are used for contrast or general statements.

Example:
한국어는 어렵다. → “Korean (in general) is difficult.”
한국어가 어렵다. → “Korean is difficult.” (Focusing on Korean itself, rather than a comparison.)

See also

-가, -은, -는