3.1 Word Formation & Derivation

The 語形成 (Word Formation) Task

The word-formation task (語形成, gokeisei) is 問題3 of the N2 文字・語彙 (moji-goi, 'characters and vocabulary') block and contributes roughly five items. Each item gives a short sentence with a blank attached to a base word, and you choose the affix — a prefix (接頭語, settougo) or suffix (接尾語, setsubigo) — that combines with that base to form a real Japanese word. N2 rewards knowing how a small stock of productive affixes generates hundreds of words, so the winning strategy is to learn the affix's function, not each derived word in isolation.

Prefixes of negation and degree

Four prefixes negate, and each pairs with specific bases by convention:

• 不 (fu-) — 'not / un-': 不便 (fuben, inconvenient), 不安 (fuan, uneasy), 不満 (fuman, dissatisfied).
• 無 (mu-) — 'without / -less': 無料 (muryou, free of charge), 無理 (muri, impossible), 無関係 (mukankei, unrelated).
• 非 (hi-) — 'non-': 非常識 (hijoushiki, lacking common sense), 非公開 (hikoukai, not public).
• 未 (mi-) — 'not yet': 未完成 (mikansei, unfinished), 未経験 (mikeiken, inexperienced).

For degree, 超 (chou-), 'super / ultra', intensifies: 超高層 (choukousou, super high-rise), 超満員 (chouman'in, jam-packed). The exam traps you by offering the wrong negation prefix — 無 where 不 is required, for instance. Because the pairing is fixed idiomatically (there is no 不料 or 無便), you must memorize the whole compound, not derive it logically.

Suffixes that change part of speech

Suffixes are where 語形成 is most productive. Learn what each does grammatically, not just what it means:

The exam loves the 的／性／化 trio because they change grammar. 的 yields a な-adjective, 性 yields a noun, and 化 yields a noun that famously takes する to become a verb — 自動化する (jidouka suru, to automate). So when the blank follows a noun and precedes だ or な, 的 is usually right; when it follows a noun and precedes が or を, a nominalizing 性 or 化 fits. Confusing 費 (running costs, e.g. 食費 food expenses) with 料 (a set fee, e.g. 入場料 admission fee) is a frequent slip.

Compound verbs (複合動詞)

Compound verbs (複合動詞, fukugou doushi) join a verb stem (連用形) to a second verb that adds aspect or nuance. High-yield second elements:

• 〜込む (-komu) — inward / thoroughly: 考え込む (kangaekomu, ponder deeply), 申し込む (moushikomu, apply for), 詰め込む (tsumekomu, cram in).
• 〜出す (-dasu) — sudden onset / outward: 泣き出す (nakidasu, burst into tears), 思い出す (omoidasu, recall), 降り出す (furidasu, start to rain).
• 〜切る (-kiru) — do completely / to the end: 使い切る (tsukaikiru, use up), 疲れ切る (tsukarekiru, be worn out), 言い切る (iikiru, assert flatly).
• 〜直す (-naosu) — redo to correct: やり直す (yarinaosu, do over), 書き直す (kakinaosu, rewrite).
• 〜合う (-au) — mutually: 話し合う (hanashiau, discuss together), 助け合う (tasukeau, help each other).

Note the meaning contrast the exam tests. 〜切る signals completion or exhaustion, while 〜込む signals depth or saturation: 使い切る empties something, but 使い込む means 'use for a long time' (or, in another sense, 'embezzle'). Choosing the wrong second verb flips the meaning entirely, so treat each pairing as its own vocabulary item.

A worked 語形成 item

Prompt: この計画は現実（　）ではない。('This plan is not ___.') Options: 的 / 性 / 化 / 感. The blank follows 現実 (genjitsu, reality) and precedes ではない, a slot that wants a な-adjective. Only 的 turns a noun into a な-adjective, giving 現実的 (genjitsuteki, realistic) — 'this plan is not realistic.' The distractors all fail on grammar: 現実性 (feasibility) is a noun needing が, 現実化 (realization) takes する, and 現実感 (a sense of reality) is a noun. The grammatical shape of the slot, not the surface meaning, selects the answer — internalize that and 問題3 becomes almost mechanical.

More productive suffixes and common traps

A few more suffixes appear often enough to memorize. 別 (-betsu) means 'classified by / per': 男女別 (danjobetsu, by gender), 年齢別 (nenreibetsu, by age group). 上 (-jou) means 'from the standpoint of / in terms of': 教育上 (kyouikujou, educationally), 立場上 (tachibajou, given one's position). 中 (-chuu / -juu) marks an ongoing state or whole span: 工事中 (koujichuu, under construction), 一日中 (ichinichijuu, all day long). The recurring trap in 問題3 is a real suffix attached to the wrong base: 教育的 (educational, な-adjective) and 教育上 (educationally, adverbial) both exist, but only one fits a given slot. Always let the surrounding particle and predicate — not the plausibility of the compound — pick the winner.