Only

만: "only", and the rules that come with it

만 is one of the first particles that feels genuinely useful, because "only" is a thing you want to say constantly and Korean gives you a single syllable to do it with.

Where it goes

만 (man) attaches straight to the noun, and then one of two things happens depending on what particle was already there.

It replaces the case particles. 이/가, 은/는 and 을/를 step aside:

• 물을 주세요 → 물만 주세요. (mul-man juseyo) — "Just water, please." Not 물을만.
• 제가 갔어요 → 저만 갔어요. (jeo-man gasseoyo) — "Only I went." Not 제가만.

It queues up behind the others. 에, 에서, 에게 and friends keep their place and 만 goes after them:

• 집에서만 공부해요. (jib-eseo-man gongbuhaeyo) — "I only study at home." Not 집만에서.
• 친구에게만 말했어요. (chingu-ege-man malhaesseoyo) — "I only told my friend."

The split is the same one 도 follows, so learning it once covers both particles. If the particle marks who or what, 만 takes its place. If it marks where or to whom, 만 lines up behind it.

만 vs 밖에

These both translate to "only" and they are not interchangeable. The difference is the verb.

만 takes a positive verb. 밖에 takes a negative one.

• 천 원만 있어요. (cheon won-man isseoyo) — "I have only a thousand won."
• 천 원밖에 없어요. (cheon won-bakke eopseoyo) — "I have only a thousand won."

Both sentences describe the same wallet. The second one complains about it. 만 is neutral and just states the amount; 밖에 carries the feeling that it isn't enough, and it requires the negative verb 없다 rather than 있다.

Get this backwards and the sentence breaks rather than just sounding odd: 천 원밖에 있어요 isn't a thing. There's a side-by-side page if you want more examples of the pair.

"Just" in the softening sense

만 also does the small social job that "just" does in English, taking the edge off a request.

• 잠깐만요. (jamkkan-man-yo) — "Just a moment."
• 이것만 보세요. (igeot-man boseyo) — "Just look at this one."

When 만 keeps a case particle

You'll occasionally meet 만이 or 만을 in writing, which looks like it breaks the replacement rule.

• 너만이 할 수 있어요. (neo-man-i hal su isseoyo) — "Only you can do it."

What's happening is emphasis: the case particle is added back on top of 만 to press on the point. It sounds formal and literary, and it turns up in speeches, lyrics and formal writing far more than in conversation. Recognize it, don't reach for it.