Japanese Adjectives to Adverbs: Ku for I-Adjectives, Ni for Na-Adjectives

The core idea: move the label from the thing to the action

An adjective is a label on a noun. A quiet room wears the label quiet. When you want to label an action instead, the word stays the same and only its ending changes, so that it can attach to a verb. You already know the vocabulary; you are learning one new ending for each adjective type.

A librarian might use the same word twice in a minute, once for the room and once for how she wants you to talk.

How the adverb is built

There are two regular rules and one irregular word. The adverb normally goes straight before the verb, though it can move earlier in the sentence.

Negative and tai forms end in i, so they follow the i-adjective rule as well: nai becomes naku and tabetai becomes tabetaku. You will need these as soon as you start talking about change.

Both types in action: a cooking lesson

Instructions are where adverbs earn their keep, because how you do something matters as much as what you do. A parent teaching a child to make curry gives one instruction after another, and nearly every one contains a ku or ni form. Notice that Japanese says cut small where English says cut into small pieces: the adverb describes the result of the cutting.

In speech, an adverb can stand alone as a whole utterance when the verb is obvious. Hayaku! shouted up the stairs means hurry up. Shizuka ni! from a teacher means quiet. The greeting yoroshiku onegai shimasu contains the adverb of yoroshii, good, and literally asks the listener to treat you favourably.

Minimal pairs: adjective against adverb

Each pair below differs in one ending. Watch which word the label lands on.

In the first pair the facts differ: an early train is a fixed thing on the timetable, while boarding early is about your own timing. In the second pair the facts are nearly the same, and the choice is one of focus. With na you are describing the finished characters, with ni the care you take.

Adverb plus suru and naru, in brief

The same ku and ni forms combine with suru, to make something a certain way, and naru, to become that way. Grammatically nothing new happens: the label attaches to the verb suru or naru just as it would to any other verb. Separate articles cover naru and suru in depth, so four examples are enough here. A guest at a hotel front desk and a neighbour in the corridor would use the first two.

Beyond the basics: ku forms that became nouns

A few ku forms are used so often for places, times and quantities that they have become nouns. You can tell because they take particles, which an ordinary adverb never does. Chikaku is the area nearby, tōku is somewhere far away, and ōku is a large number. Hayaku and osoku do the same for time with kara and made.

The label image bends here, and it is better to admit it: these words are no longer labels on an action but names of a place or amount. The reason to learn them as a group is practical. Eki no chikai is wrong, and ōi hito is not how you say many people. Ōi and sukunai are rarely placed directly before a noun, so the noun form with no takes over.

Beyond the basics: yoku, sugoku, hidoku and meanings that drift

Some adverbs wander from the meaning of their adjective. Yoku is the important one. From good it gives well, and from doing something fully it extends to doing it many times, so it also means often. It also appears in fixed phrases of welcome and praise, such as yoku dekimashita, well done.

Sugoi means amazing or dreadful, but sugoku is mostly a plain intensifier, very. Hidoi means cruel or awful, and hidoku means severely or badly, again as a measure of degree, always for something unwelcome. Karuku, from karui, light, often means casually or as a small amount.

Neighbours: the kute form and ready-made adverbs

The form most often confused with ku is kute, and with ni it is de. Kute and de are connectors: they join an adjective to a further description and mean and. Ku and ni attach the adjective to a verb. Yasukute oishii is cheap and tasty, two labels on one restaurant. Yasuku kaimashita is bought cheaply, one label on the buying.

Japanese also has many words that are born adverbs, such as yukkuri, sugu, totemo and hakkiri. They need no ending at all. Adding ni to them is a common slip.

Common mistakes with ku and ni adverbs

The first mistake is leaving the adjective unchanged. Hayai hashirimasu is wrong. English fast is both adjective and adverb, so the need for a new ending is easy to miss. Say hayaku hashirimasu.

The second is making the adverb of ii by rule. Ii dekimashita and iku dekimashita are both wrong. The forms of ii are built on yoi: yoku dekimashita.

The third is treating kirei as an i-adjective. Kireku kakimasu is wrong. The final i is part of the word, not an ending. Say kirei ni kakimasu.

The fourth is crossing the endings: hayai ni and shizukaku are wrong. Check the adjective type first. If it takes na before a noun, it takes ni before a verb.

The fifth is adding ni to a ready-made adverb. Yukkuri ni hanashimasu is wrong, an over-application of the na-adjective rule. Yukkuri hanashimasu is complete.