Compound Adjectives in Japanese (複合形容詞): The V-Stem + Adjective Pattern
Compound adjectives in Japanese (複合形容詞, fukugō keiyōshi) are い-adjectives built by attaching an adjective head to the 連用形 (masu-stem) of a verb. The result is a new い-adjective that inflects from the head.12 Once you see the recipe, words like 読みやすい, 信じがたい, and 蒸し暑い look less like separate vocabulary items and more like instances of one pattern with a fixed tail.
Overview
This article is the conceptual umbrella for the V-stem + い-adjective family at JLPT N4. It names the recipe, sorts the heads into productive (open-class) and lexicalized (frozen) groups, and points to dedicated pattern articles for a deeper look at each productive suffix.345
Japanese 複合動詞 (compound verbs) are far more numerous than 複合形容詞.2 The two are sibling constructions and share the same joining slot, but compound adjectives form a smaller and more selective set.
What "compound adjective" means here
複合形容詞 covers any adjective built from two words: a left-hand stem (a verb, noun, or another adjective) plus an い-adjective head attached to it.12 This article restricts scope to the verb-stem + い-adjective subtype, which is what most learners encounter at N4 through 〜やすい and 〜にくい.
Two other subtypes sit in the same family but fall outside the V-stem recipe. Noun + adjective compounds like 青白い "pale, bluish-white" and 力強い "powerful, reassuring" join a noun stem to an い-adjective head.21 Adjective + adjective compounds like 狡賢い "crafty-clever" join two adjective stems. They are mentioned here only to make the boundary of the V-stem subtype clear. They are not the focus.
Why the V-stem is the joining slot
The 連用形 (ren'yōkei, also called the masu-stem or i-stem) is Japanese's general joining form in word formation.67 Compound verbs (V1 連用形 + V2) and compound adjectives (V 連用形 + adj) both exploit it.687 If you already control the 連用形 from learning ます-form, you already control the input side of every compound adjective in this article.
Where this article sits in J-Compass
The umbrella concept (V-stem + adjective as a recipe) is structural, not a discrete JLPT grammar point. The pattern walkthroughs for each productive head live in their own dedicated articles. This page names the family, explains the mechanics, and points you to the per-suffix pages. It does not drill any one suffix.
Form: how V-stem + adjective is built
The recipe in one line
Take the verb's 連用形 (the form before ます) and attach an い-adjective head to it. The result is a new い-adjective.451
読みやすい本です。5
"It's a book that's easy to read."
この魚は食べにくいです。4
"This fish is hard to eat."
Bunpro states the morphology plainly: にくい "attaches to the ます stem of verbs" and turns the verb into "difficult to (A)." やすい likewise "attaches to verb stems" and yields "easy to do."45
Conjugation inheritance from the head
A V-stem + い-adjective compound inflects as an い-adjective, regardless of the verb's class.45 Past, negative, て-form, and adverbial く-form all come from the adjective head. They do not come from the verb stem.
食べやすかったです。5
"It was easy to eat."
読みにくくないです。4
"It isn't hard to read."
The compound also modifies nouns directly, with no の, just like any い-adjective: 食べやすい果物 "easy-to-eat fruit."4
In a compound adjective, the verb stem is fixed in 連用形 and stays fixed. Tense, negation, politeness, and adverbial form all live on the adjective head. If you conjugate the verb instead, as in the ungrammatical 食べましたやすい, the compound has slipped out of shape.
Accent and reading notes
Tokyo Japanese gives adjective-headed compounds a penultimate accent pattern, while Kansai Japanese gives them an antepenultimate one.10 Both are subsets of the patterns available to non-compound adjectives in the same dialect. Compound adjective accentuation is more restricted than non-compound adjective accentuation.10
Reading shifts also differ across the productive / lexicalized split. Lexicalized compounds can show rendaku on the head consonant, as in 高い → 名高い nadakai (t → d).111 Productive compounds with 〜やすい, 〜にくい, and 〜がたい do not voice their initial consonant; the suffix surface form is fixed.4512 The head 〜づらい is the special case. It begins with づ rather than つ because the suffix itself is the rendaku product of つらい tsurai.13
The productive vs. lexicalized split
The central question for this whole family is whether a compound is built on the fly from a live rule or stored whole in the lexicon. The same recipe lies behind both, but only one side is open to new coinages.
Productive (open-class) heads: any V-stem can take them
The productive heads attach to the 連用形 of almost any compatible verb to form a new い-adjective on the fly.451213 The core inventory:
| Head | Meaning | Register / JLPT |
|---|---|---|
| 〜やすい | easy to (do) | N4, everyday5 |
| 〜にくい | objectively hard to (do) | N4, everyday4 |
| 〜づらい | hard / painful for the speaker to (do) | N3-ish, subjective13 |
| 〜がたい | nearly impossible to (do) | N2, formal / literary12 |
| 〜たい | want to (do) (speaker's own desire) | N5, everyday3 |
Productivity shows up in three places: the head accepts unfamiliar verbs, the meaning is transparent (V + ease / difficulty / desire), and corpora like BCCWJ document the patterns across many genres.1415
漢字は覚えにくい。4
"Kanji are hard to memorize."
このペンは書きやすい。5
"This pen is easy to write with."
彼の犯罪は許しがたい。12
"His crime is unforgivable."
寿司が食べたいです。3
"I want to eat sushi."
Lexicalized (frozen) compounds: memorize as single words
Lexicalized compounds carry the V-stem + adjective shape as etymology, not as a live rule.1 They have single-entry listings in major monolingual dictionaries like Shin Meikai. Their meaning has drifted from the literal sum of parts, and you cannot swap in a different verb stem and expect the result to make sense.
- 名高い nadakai "famous" is 名 "name" + 高い "high," with rendaku t → d; treated as one lexical item.11
- 蒸し暑い mushiatsui "hot and humid" is the 連用形 of 蒸す "to steam" + 暑い "hot," listed in Shin Meikai as a single headword.16
- 力強い chikara-dzuyoi "powerful, reassuring" is a noun-stem compound rather than a V-stem compound, listed here because learners meet it in the same lexicalized family.1
- 堅苦しい katakurushii "stiff, formal" uses 苦しい as a frozen suffix-like head, with the compound listed as a single lexical item.1
彼は名高い学者です。11
"He is a renowned scholar."
東京の夏は蒸し暑い。16
"Tokyo summers are hot and humid."
The diagnostic checklist
Use three tests together to sort a candidate compound as productive or lexicalized.
- Substitution test. A productive head accepts a fresh, unfamiliar verb stem and still gives a transparent meaning. A lexicalized item resists substitution.1
- Dictionary test. A lexicalized compound has a single-entry listing in a major monolingual dictionary (e.g. Shin Meikai). A productive combination usually does not.1116
- Transparency test. Productive compounds mean V + ease / difficulty / desire. Lexicalized compounds carry idiomatic meaning that is not the sum of parts (力強い ≠ "strength-high"; 名高い ≠ "name-high").111
Borderline cases learners ask about
〜やすい and 〜にくい combine freely with stative verbs (わかりやすい "easy to understand," 見えにくい "hard to see"). Productivity is not limited to action verbs.45
〜たい sits between two analyses. Some grammars treat it as an inflectional suffix (an auxiliary verbal); others treat it as a member of the compound-adjective family because it conjugates as an い-adjective and attaches to the 連用形.39 Both analyses appear in standard references. J-Compass keeps the dual framing rather than picking a side.
A phrase like 居心地のよい / 居心地がよい uses よい as a free adjective head following a noun phrase, not the V-stem + adj recipe. This is a phrasal use of よい rather than a true compound adjective. It is mentioned here only because the shape can fool readers into parsing it as one.
The productive heads at a glance
This section names the productive heads and shows what each one contributes to the family. The detailed walkthroughs (particle behavior, register, pitfalls, scope of acceptable verbs) belong to dedicated pattern articles in the sentence-patterns series. Treat the lines below as a map, not a tutorial.
〜やすい / 〜にくい / 〜づらい / 〜がたい (ease and difficulty)
〜やすい (N4) is the everyday "easy to do" head.5 〜にくい (N4) is the everyday "objectively difficult / hard to do" head, where the difficulty comes from skill level or properties of the object.4 〜づらい (around N3) means "hard to do because it causes the speaker distress" and comes etymologically from つらい "bitter, painful."13 〜がたい (N2) expresses near-impossibility, often with a psychological or moral edge, and has a formal, literary register.12
Together, the four form a difficulty ladder ordered roughly by both intensity and register. The side-by-side usage walkthrough belongs to its own pattern article.
〜たい (own desire)
〜たい attaches to the masu-stem to express the speaker's own desire and conjugates as an い-adjective.3 In plain declarative use it is restricted to first-person subjects. In questions it shifts to second-person. For an observed third-person desire, Japanese reaches for 〜たがる or 〜たそうだ.17 The full subject-restriction story has its own dedicated pattern article.
Why this page stops at the recipe level
Each productive head has its own particle behavior, register quirks, and pitfalls. Compressing five of them into one umbrella page would either short-change them or make the article too long to be useful. The umbrella names the family; the pattern pages teach the usage.
Nuance and usage contexts
Productive heads are register-flexible
〜やすい and 〜にくい are comfortable in everyday spoken and written Japanese.45 〜づらい is more subjective than 〜にくい: "something ~nikui is something that's generally difficult for anyone to do, objectively difficult, while something that's ~dzurai is difficult for you to do, because it implies it causes you distress."13 〜がたい has a high, literary register and carries the psychological near-impossibility framing of MLC's gloss.12
The ladder is informal but useful for choosing a head. Pick the lowest rung that captures the difficulty you mean, and raise the register only if the writing context calls for it.
Lexicalized compounds carry idiom-strength meaning
力強い is "powerful, reassuring," not literally "strength-high." The compound carries idiomatic force that the parts alone do not.1 蒸し暑い is "hot and humid / muggy," not "steam-hot" in any compositional sense. It is simply the standard word for muggy weather.16 名高い is "famous, renowned," not "name-high." The meaning sits in the lexicon, not in the morphology.11
For a productive compound, parsing V-stem + head is the right reflex. For a lexicalized compound, the same reflex produces a wrong gloss. When a dictionary lists the word as a single headword, treat it as vocabulary, not as a live composition.
The parallel with compound verbs
Compound verbs (V1 連用形 + V2) and compound adjectives (V 連用形 + adj) are sibling constructions, both built on the 連用形 as the joining slot.687 NINJAL's Compound Verb Lexicon (Kageyama, lead) is the canonical reference for the productive V1+V2 inventory. Its existence reflects how central the 連用形 is as a word-formation pivot in Japanese.8
Good to know
Why the head is always an い-adjective, never a な-adjective
な-adjectives are noun-like and do not attach directly to V-stems. There is no productive pattern "V-stem + しずか" or "V-stem + 元気." The slot after a 連用形 wants either another verb (yielding a compound verb) or an い-adjective (yielding a compound adjective).
な-adjectives sit one syntactic layer further out and behave more like nouns plus a copula. Treat the い-adjective restriction as a structural property of the pattern, not as a list of exceptions to memorize.12
Reading aids when you meet an unfamiliar compound
When you see a compound adjective with no furigana, segment it at the head, then read the V-stem from the masu-form. With 信じがたい, identify がたい as the head and read 信じ as the 連用形 of 信じる "to believe," giving "hard to believe." With 聞き苦しい, identify 苦しい as the head and 聞き as the 連用形 of 聞く "to listen." Then recognize the compound as lexicalized: it is in dictionaries as one word, and its meaning is closer to "unpleasant to hear" than to "listen-painful."
Productivity is not unlimited
Even open-class heads come with constraints. 〜たい is restricted to first- and second-person subjects depending on sentence mood.17 〜がたい sits in formal, often emotional or moral territory. MLC describes it as "psychologically difficult," which fits the impression that it resists purely physical or volitional predicates, though the formal syntactic restriction is not laid out in primary sources within easy reach.12 The productive class is open but still shaped. Expect each head to refuse some verbs, and let the dedicated pattern articles fill in the specific limits.
〜苦しい and 〜よい look productive but are not
〜苦しい turns up inside lexicalized compounds such as 堅苦しい "stiff, formal," which can make it look like an open-class "discomfort" head.1 Learners are better served by treating each such compound as a lexical item rather than producing new 〜苦しい coinages on demand. The formal status of 〜苦しい as a closed versus very narrowly productive head is a teaching observation more than a firmly documented constraint.
A similar shape trap: 〜よい / 〜いい sitting after a noun phrase plus の or が. In that frame, よい is a free adjective head attached to a noun phrase, not a suffix attached to a V-stem. Recognizing the difference keeps you from parsing such phrases as compound adjectives of the V-stem + adj kind.
〜づらい comes from つらい "painful, bitter"
The reading づ rather than つ is rendaku in the compound. Knowing the etymology explains why 〜づらい always carries an emotional-pain flavor. This is not an idiomatic accident, but the source meaning showing through.13 If you can feel つらい inside 〜づらい, you will choose it more accurately when difficulty has a subjective, distressed edge.
名高い preserves rendaku that productive heads do not show
高い "high" becomes 高い as a suffix with rendaku t → d, yielding 名高い nadakai.111 The voicing is a fossilized phonological change marking lexicalization.
Productive 〜やすい, 〜にくい, and 〜がたい never voice their initial consonant in compounds. Voicing on the head, when it appears, is one signal of a frozen lexical item rather than a live composition.
A Y-N-Z-G mnemonic for the difficulty ladder
Yasui (easy) – Nikui (objectively hard) – Zurai (painfully hard) – Gatai (almost impossible). Reading the four heads as a single mnemonic ladder makes them easier to recall as a set. It also lines up intensity with register: the head at the top of the ladder is the most literary one. Bunpro and MLC teach the difficulty contrast in the same direction.412
Conjugating the verb instead of the adjective head
A common pitfall is marking tense or politeness on the verb stem, as in 食べましたやすい. The compound is an い-adjective, so tense and politeness live on the adjective head. The correct form attaches the past-tense morphology to やすい:
食べやすかったです。5
"It was easy to eat."
Choosing 〜にくい when 〜づらい is the better fit
A learner who wants to say "It's emotionally hard for me to tell him how I really feel" may default to 〜にくい, producing 彼に本音を言いにくい. That version sounds like objective or skill-based difficulty. For emotional reluctance, the better head is 〜づらい, which carries the speaker-distress nuance inherited from つらい:
彼に本音を言いづらい。13
"It's emotionally hard to tell him how I really feel."
Using 〜たい for a third-person subject in plain narrative
In plain declarative narrative, 〜たい reports the speaker's own desire. So 妹はアイスを食べたい reads as wrong (or at best as free indirect style). For an observed third-person desire, Japanese uses 〜たがる / 〜たがっている (or 〜たそうだ for "looks like they want to"):
妹はアイスを食べたがっている。17
"My little sister wants to eat ice cream."
〜がたい in casual conversation
〜がたい is formal and literary. In everyday spoken Japanese, 〜にくい (objective) or 〜づらい (subjective) is the natural choice. 〜がたい in a casual exchange sounds stiff or self-consciously bookish, even when the psychological near-impossibility reading fits.12
See also
- The Japanese Verb Stem (連用形): The Masu-Stem and Its Uses
- Compound Verbs in Japanese (複合動詞): The V1-Stem + V2 Pattern
- ～出す, ～切る, ～込む, ～直す in Japanese: V2 Aspect Suffixes (Sudden Onset, Completion, Inward/Depth, Redo)
- ～始める, ～終わる, ～続ける in Japanese: Beginning, Ending, and Continuing an Action
- Pitch Accent for Japanese Verbs and Adjectives: The Binary Class Rule and Conjugation Shifts
- Rendaku in Kanji Compounds: Why 紙 Becomes -gami