Subject Particles 이/가 in Korean

In Brief

Attach 이 after a noun ending in a consonant and 가 after a noun ending in a vowel: 물이 “water” but 날씨가 “the weather.” These particles mark the subject—the person or thing that acts, exists, or has the quality described—and often highlight the answer to “who?” or “what?”

Overview

Korean uses short words called particles after nouns. A particle shows what job the noun has in the sentence. 이/가 marks a noun as the subject: in plain terms, who or what performs an action, exists, or is described. In 고양이가 자요 (“The cat sleeps”), 고양이 is what sleeps, so it takes 가.

This is a core A1 pattern, but it differs from English in two important ways. English mainly shows grammatical roles through word order: “The dog sees the child” changes meaning if the two nouns switch places. Korean particles label those roles directly. Korean also often leaves out a subject when the context makes it obvious, while English usually requires one: 학생이에요 can mean “I’m a student,” “He’s a student,” or “She’s a student,” depending on the conversation.

The choice between 이 and 가 is purely about the final sound of the noun. The more challenging choice is often between subject marking 이/가 and topic marking 은/는. Start by learning the form rule and using 이/가 for the person or thing specifically identified by a question. The finer contrast comes later in this article.

How It Works

Choose the form by the final sound

이 and 가 have the same grammatical function. Korean uses two forms so the particle fits smoothly after the noun.

End of the noun	Particle	Combination	Meaning
Consonant (a final consonant, or 받침)	이	물 + 이 → 물이	water + subject marker
Vowel (no final consonant)	가	날씨 + 가 → 날씨가	weather + subject marker

Look at the last written syllable:

• 책 ends with the final consonant ㄱ, so use 책이.
• 사람 ends with the final consonant ㅁ, so use 사람이.
• 집 ends with the final consonant ㅂ, so use 집이.
• 학교 ends in the vowel ㅛ, so use 학교가.
• 친구 ends in the vowel ㅜ, so use 친구가.
• 의자 ends in the vowel ㅏ, so use 의자가.

A final ㄹ still counts as a consonant: 서울이, not 서울가. Choose from the Korean form, not from an English translation or romanization.

Attach the particle directly

Write the particle as part of the same spacing unit as the noun:

• 학생이 왔어요. — A student came.
• 버스가 와요. — The bus is coming.

Do not put a space between the noun and particle. There is normally a space after the complete noun phrase: 학생이 왔어요, not 학생 이왔어요.

If the noun has a modifier, attach 이/가 to the end of the entire noun phrase:

• 새 학생이 왔어요. — A new student came.
• 제가 산 책이 재미있어요. — The book I bought is interesting.

What can the marked subject do?

The subject is not limited to an active “doer.” It can have several roles:

1. Perform an action: 민수가 요리해요. — Minsu cooks.
2. Have a quality: 날씨가 좋아요. — The weather is good.
3. Exist or be present: 방에 사람이 있어요. — There is a person in the room.
4. Be needed, liked, or known: 물이 필요해요. — Water is needed. / I need water.

The fourth pattern can feel unusual to an English speaker. Korean predicates (the part saying something about the subject) do not always organize their participants like English verbs. For example, in 저는 커피가 좋아요, 저는 sets “as for me” as the topic, while 커피가 is what is good or pleasing. The natural English translation is “I like coffee,” but attaching an English-style object marker to 커피 would not preserve the Korean structure.

Use 이/가 to identify who or what

이/가 is especially natural when the subject is the requested or focused information:

• 누가 왔어요? — Who came?
• 지수가 왔어요. — Jisu came.

The question asks for the identity of the subject, and the answer supplies it. The same effect appears when correcting an assumption or emphasizing one choice:

• 제가 할게요. — I’ll do it.
• 이 버스가 서울에 가요. — This bus goes to Seoul.

Important pronoun contractions

A few common combinations contract rather than following the visible pattern mechanically:

Base form	With 가	Meaning
나	내가	I (informal/plain)
저	제가	I (polite/humble)
너	네가	you (informal)
누구	누가	who

Forms such as 나가 and 저가 are not the standard subject-marked forms of these pronouns. In speech, 네가 is often pronounced closer to 니가 to distinguish it from 내가, though standard spelling remains 네가.

Basic contrast with 은/는

Both sets can follow a noun, but they organize the message differently.

Particle	Beginner-friendly function	Typical question
이/가	Identifies or focuses the subject	Who/what is it? Who/what did it?
은/는	Establishes a topic or contrast: “as for…”	What can you say about this topic?

Compare:

• 고양이가 귀여워요. — The cat is cute. / It is the cat that is cute.
• 고양이는 귀여워요. — As for the cat, it is cute. (Possibly contrasting it with something else.)

“New information uses 이/가; known information uses 은/는” is a useful first clue, not an absolute rule. Speakers choose particles according to what they present as the topic, what they focus, and what contrasts are active in the conversation.

Examples in Context

Korean	English	Note
날씨가 좋아요.	The weather is good.	날씨 ends in a vowel.
물이 필요해요.	Water is needed. / I need water.	물 ends in ㄹ.
학생이 질문했어요.	A student asked a question.	The subject performs the action.
버스가 왔어요.	The bus arrived.	The arriving item is the subject.
방에 고양이가 있어요.	There is a cat in the room.	The thing that exists takes 이/가.
시간이 없어요.	There is no time. / I don’t have time.	The absent thing takes 이/가.
누가 왔어요?	Who came?	누구 + 가 contracts to 누가.
제가 할게요.	I’ll do it.	저 + 가 contracts to 제가; the speaker volunteers.
어느 식당이 좋아요?	Which restaurant is good?	The question asks which one has the quality.
이 식당이 좋아요.	This restaurant is good.	Identifies the restaurant in answer to the question.
저는 커피가 좋아요.	I like coffee.	저는 is the topic; coffee is marked with 가.
동생이 키가 커요.	My younger sibling is tall.	Literally, “As for the sibling, the height is big”; see advanced use.
비가 와요.	It’s raining.	Literally, rain comes/falls; 비 is the subject.
한국어가 재미있어요.	Korean is interesting.	The thing described as interesting takes 가.

Common Mistakes

Choosing by meaning instead of the final Korean sound

• Wrong: 책가 재미있어요.
• Right: 책이 재미있어요.
• Why: 책 ends in the consonant ㄱ, so it takes 이. Meaning does not determine the form.

Treating pronouns as regular combinations

• Wrong: 저가 할게요.
• Right: 제가 할게요.
• Why: 저 + 가 contracts to 제가. Likewise, use 내가, 네가, and 누가.

Copying English subject–verb structure too literally

• Wrong: 저가 커피를 좋아요.
• Right: 저는 커피가 좋아요. — I like coffee.
• Also right: 저는 커피를 좋아해요. — I like coffee.
• Why: The adjective-like predicate 좋아요 commonly marks the liked thing with 이/가. The verb 좋아해요 takes an object with 을/를. These are different Korean constructions even when English translates both as “like.”

Using 이/가 and 은/는 together on the same noun

• Wrong: 고양이가 는 귀여워요.
• Right: 고양이가 귀여워요. / 고양이는 귀여워요.
• Why: Choose the particle that matches the noun’s role in the message. Do not stack 이/가 and 은/는 on the same noun in this basic pattern.

Adding a space before the particle

• Wrong: 친구 가 왔어요.
• Right: 친구가 왔어요.
• Why: Korean case particles are written attached to the noun.

Assuming every English subject must appear in Korean

• Unnatural in context: 저는 학생이에요. 저는 서울에 살아요. 저는 한국어를 공부해요.
• More natural after the first sentence: 저는 학생이에요. 서울에 살아요. 한국어를 공부해요.
• Why: Once the subject is clear, Korean commonly omits it. Repeating it is grammatical but can sound heavy or unnecessarily contrastive.

Usage Notes

In conversation, subjects and their particles are often omitted when everyone knows who or what is being discussed. A server asking 뭐가 필요하세요? (“What do you need?”) may hear simply 물 주세요 (“Water, please”), not a complete sentence with every role marked. Learn the full marked form first; omission becomes easier to judge with exposure.

The particle often carries information structure that English conveys through stress or wording. 제가 했어요 may mean “I did it” with focus on I, depending on context. English can emphasize the subject by voice stress; Korean can use 이/가, context, and intonation together.

Politeness does not change 이 into 가 or vice versa. Those forms depend only on the noun’s final sound. Honorific verb endings and honorific vocabulary are separate choices. In respectful reference to a person, however, you may encounter the honorific subject particle 께서, discussed below.

Beyond the Basics / Advanced Use

You do not need to master these patterns at A1, but recognizing them will prevent the beginner rule from becoming too rigid.

이/가 versus 은/는 is a discourse choice

The contrast is not equivalent to English “a” versus “the.” Either particle can occur with a person or thing already known to the listener. Consider a story opening with 옛날에 한 왕이 살았어요 (“Long ago, a king lived…”): 이 introduces the king as the subject. Later, 왕은 can continue with the king as the established topic. But a speaker may return to 왕이 when identifying the king as the one who performed a particular action.

Likewise, 은/는 can create an implied contrast:

• 오늘은 날씨가 좋아요. — As for today, the weather is good.

Here 오늘은 frames the time as the topic or contrast, while 날씨가 remains the grammatical subject of “is good.” Different particles can therefore appear in one sentence because they mark different phrases.

Subjects inside larger clauses

Korean often uses 이/가 for a subject inside an embedded or modifying clause, even when the whole sentence has another topic:

• 저는 비가 오는 날을 좋아해요. — I like days when it rains.

저는 is the topic of the whole sentence. Inside 비가 오는 (“when/on which rain falls”), 비가 is the subject of 오는. This becomes increasingly important as sentences grow longer.

So-called double-subject constructions

Sentences such as 코끼리가 코가 길어요 (“Elephants have long trunks”) and 동생이 키가 커요 (“My younger sibling is tall”) contain two 이/가 phrases. Analyses differ in their technical labels, but the learner-friendly idea is that the first phrase establishes the larger entity and the second names the relevant part or property. Do not force a word-for-word English structure onto them.

아니다 and 되다

With 아니다 (“to not be”), the noun being denied commonly takes 이/가:

• 저는 학생이 아니에요. — I am not a student.

With 되다 (“to become”), the resulting role or state commonly takes 이/가 as well:

• 의사가 되었어요. — [Someone] became a doctor.

These patterns are worth learning as complete chunks rather than deriving them from English “be” or “become.”

Honorific 께서 and colloquial omission

께서 is an honorific subject marker used when showing respect to the subject:

• 선생님께서 오셨어요. — The teacher has arrived.

It often appears with honorific verb marking, here 오셨어요. In ordinary speech, 선생님이 오셨어요 is also common and can still be respectful because the verb carries honorific marking.

At the other end of the register scale, casual speech may omit particles: 누구 왔어? instead of 누가 왔어? Such omission is common but context-sensitive. Keep 이/가 in your own beginner sentences until you have a feel for when native speakers leave it out.

Practice Tips

1. Train the sound choice separately. Take ten nouns and say each with the particle: 책이, 문이, 물이; 학교가, 의자가, 친구가. Check only the final Korean syllable.
2. Build question-and-answer pairs. Ask 누가 왔어요? and answer with different focused subjects: 민지가 왔어요, 선생님이 왔어요, 제가 왔어요. This makes the identifying function concrete.
3. Notice two things while listening. First, circle every written 이/가 and identify its noun. Then notice where Korean leaves out a subject that an English translation supplies. This prevents you from assuming that every English “I,” “he,” or “it” needs a Korean equivalent.

Related Concepts

• Prerequisite: Basic Sentence Structure — review how Korean predicates normally come at the end of the sentence.
• Compare next: Topic Particle 은/는 — learn how Korean establishes a topic and creates contrast.