Regular vs Irregular Predicates: The Big Picture

The word "irregular" scares learners more than it should. In Korean, an irregular predicate is not a form you have to memorize whole, the way English makes you memorize go → went → gone. It is a stem whose final letter performs a small, rule-governed sound change when a certain kind of ending attaches — and once you know the class, the change is fully predictable. This page gives you the shape of the entire system so that, from now on, you stop asking "is this word irregular?" and start asking a far more useful question: "what is the last letter of this stem?"

First, the reframing English speakers need

An English irregular verb is unpredictable by design: nothing about the shape of think tells you the past is thought. Korean irregulars are the opposite. Membership is decided almost entirely by the final consonant or vowel of the stem, plus a short exception list you can count on your fingers. So "irregular" here really means regular in a second, smaller pattern — a phonological rule that reshapes the boundary between the stem and the ending.

Two facts unlock everything else on this page:

1. You read the last jamo of the stem, not the whole word. 덥다 ("is hot") and 듣다 ("hear") behave differently only because one ends in ㅂ and the other in ㄷ.
2. Adjectives conjugate exactly like verbs. Korean descriptive verbs — what English calls adjectives — inflect through the same endings and the same irregular rules. 덥다 ("is hot," an adjective) and 걷다 ("walk," a verb) run through identical machinery. Never treat "adjective" as a reason a word behaves differently.

The eight classes at a glance

Here is the whole system in one table — each class named by the stem-final jamo that triggers it, with a model predicate and the form it produces before a vowel ending.

Everything else in the irregular-verb section is just these eight rows, one page each. Let's see the most important of them in a real sentence so the pattern feels concrete rather than abstract.

Each class, once, in the wild

ㅂ — the biggest and most useful class. Stem-final ㅂ softens to 우 before a vowel. Almost every weather and sensation adjective lives here.

ㄷ — the ㄷ that turns into ㄹ. A handful of verbs, most notably 듣다 ("hear/listen") and 걷다 ("walk"), swap their final ㄷ for ㄹ before a vowel.

ㅅ — the ㅅ that just disappears. The stem-final ㅅ drops, but — crucially — the two vowels left behind do not contract. 짓 + 어요 becomes 지어요, never ×져요.

르 — the doubling ㄹ. Stems ending in 르 (모르다, 부르다, 빠르다) grow an extra ㄹ: 모르 + 아요 → 몰라요.

으 — the most "regular" irregular of all. A stem-final ㅡ simply drops before -아/어. This is so predictable that many linguists don't even call it irregular.

ㄹ — the vanishing ㄹ. Verbs like 살다 ("live") and 알다 ("know") drop their ㄹ before endings starting with ㄴ, ㅂ, ㅅ, or 오 — which is why the honorific of 살다 is 사세요, not ×살으세요.

ㅎ — the fusing ㅎ. Almost every color and "this/that kind of" adjective (빨갛다, 그렇다, 어떻다) drops its ㅎ and fuses the leftover vowel into ㅐ before an ending.

러 — the tiny four-member club. A rare set (이르다 "reach," 푸르다 "be blue," 누르다 "be yellow") changes the ending's 어 to 러 rather than touching the stem. You will meet it a handful of times ever, but recognize it so it doesn't ambush you.

The trap: "looks hard" is not a class

Here is where English speakers routinely go wrong. They see a stem that "looks difficult" — an unfamiliar shape, a double consonant, a Sino-Korean root — and assume it must be irregular. It doesn't work that way. Membership is decided by the final jamo plus a short exception list, and some of the most ordinary-looking words are perfectly regular:

닫다 ("close") ends in ㄷ but is regular; 좁다 ("narrow") ends in ㅂ but is regular; 웃다 ("laugh") ends in ㅅ but is regular. Their final consonants simply liaise onto the following vowel with no change at all. So the final jamo tells you which class to check, and a short list of exceptions tells you whether an individual word is actually a member. That two-step — read the letter, then check the list — is the entire skill.

Why "when" matters as much as "how"

Notice that every example above changed before a vowel-initial ending (-아/어요). That is not a coincidence. Irregular stems only fire in specific ending environments; before other endings they sit perfectly still:

덥다 becomes 더워요 before -아요, but stays 덥고 before -고. Knowing when a stem changes is exactly as important as knowing how — and it is governed by a clean three-way sorting of endings. That is the very next page: When Irregulars Fire: The Three Ending Environments. After that, the reference table puts all eight classes side by side as a hub you can return to.

Common Mistakes

1. Assuming a stem is irregular because it looks unusual. Class membership is a vocabulary fact keyed to the final jamo, not a vibe. 받다 ("receive") ends in ㄷ but is regular.

2. Applying the sound change before a consonant ending. Irregulars stay put before -고, -지, -게, -다.

3. Contracting the two vowels in a ㅅ-irregular. The ㅅ drops, but the vowels do not fuse.

4. Forgetting that adjectives are irregular too. 춥다 ("is cold") is a ㅂ-irregular adjective, and it conjugates like any ㅂ verb.

Key Takeaways

• "Irregular" in Korean means a small, predictable sound change keyed to the stem's final jamo — not an unpredictable memorized form.
• There are eight classes: ㅂ, ㄷ, ㅅ, 르, 으, ㄹ, ㅎ, and the tiny 러 set.
• Adjectives conjugate exactly like verbs — never treat word class as a reason for different behavior.
• Membership is the final letter plus a short exception list: 닫다, 좁다, 웃다, 받다 look irregular but are regular.
• The change fires only in certain ending environments — read the trigger-endings page next.