Japanese Adjective Conjugation Chart: Every Form of I and Na Adjectives

Two types, two systems

Every Japanese adjective belongs to one of two types. I-adjectives end in the syllable i in their dictionary form: takai, samui, oishii, atarashii. Na-adjectives take na when they sit in front of a noun: shizuka na heya, genki na kodomo, benri na basho. The label tells you which conjugation system to use, and it is the only thing you have to memorise per word.

The trap is that some na-adjectives end in i: kirei, yūmei, kirai, teinei. They are still na-adjectives, because the i is part of a kanji reading rather than an inflectional ending. Kirei is 綺麗, and it becomes kirei na hana, kirei datta, kirei ja nai. If you conjugate it as kirekatta you have made the single most common adjective mistake in the language.

I-adjectives change their own ending. Na-adjectives never change: instead the copula that follows them does the work, using exactly the forms you already know from desu and da with nouns. So learning the na-adjective chart is really revising the copula.

The full conjugation chart

The chart below uses takai, expensive or tall, for i-adjectives and shizuka, quiet, for na-adjectives. Plain forms are what you use with friends, inside clauses and before nouns. Polite forms are for strangers, customers and superiors. For i-adjectives the polite form is simply the plain form plus desu; for na-adjectives the polite forms replace da with desu and use the longer negatives.

Two things to notice. First, the i-adjective past negative is just the negative kunai treated as a new i-adjective and put into the past: kunai becomes kunakatta, exactly as takai becomes takakatta. Second, ja nai and ja nakatta are contractions of de wa nai and de wa nakatta; the longer forms are more formal and are what you will see in writing.

Present and past: the forms you use every day

The past tense is where English speakers slip. Because English puts the past on the verb to be, it feels natural to say takai deshita, but Japanese carries tense inside the i-adjective, so the correct polite past is takakatta desu. Desu here is a politeness marker only and never changes form. Once that clicks, oishikatta desu, samukatta desu and tanoshikatta desu come easily, and they are among the most useful sentences a learner has, because they let you say how something was.

Na-adjectives behave like nouns, so the past really is deshita: shizuka deshita, genki deshita, taihen deshita. Plain past is datta: shizuka datta, taihen datta. The plain forms matter more than beginners expect, because they are the forms you use inside longer sentences: shizuka datta kara, because it was quiet; takakatta kedo, it was expensive but.

Negatives and past negatives

The i-adjective negative drops i and adds kunai: takakunai, samukunai, oishikunai. Kunai is itself an i-adjective, which is why it can go into the past as kunakatta and take desu for politeness. There is an older polite negative, takaku arimasen, which is still correct and sounds slightly formal; takakunai desu is what most people say.

Na-adjectives use the copula negative. In speech, ja nai and ja nakatta: shizuka ja nai, genki ja nakatta. In polite speech, ja arimasen and ja arimasen deshita, or the fuller de wa arimasen in formal contexts. The negative is also where softeners go: amari shizuka ja nai, not very quiet; zenzen takakunai, not expensive at all. Amari and zenzen almost always call for a negative ending, so hearing one at the start of a sentence lets you predict the end.

Te form, adverb and conditional

The te form joins an adjective to whatever comes next. For i-adjectives it is kute; for na-adjectives it is de, the te form of the copula. Yasukute oishii is cheap and tasty; shizuka de kirei is quiet and beautiful. The same form gives a reason: atsukute nemuremasen, it is hot so I cannot sleep. Only the last adjective in a chain carries the tense, so yasukute oishikatta means it was cheap and tasty.

The adverb form turns an adjective into a description of how something is done. I-adjectives take ku: hayaku hanasu, speak fast; ōkiku kaku, write big. Na-adjectives take ni: shizuka ni suru, be quiet; kirei ni sōji suru, clean thoroughly. The ku and ni forms also combine with naru, to become, and suru, to make: samuku natta, it got cold; heya o kirei ni shita, I tidied the room.

The conditional is kereba for i-adjectives and nara for na-adjectives: yasukereba kaimasu, if it is cheap I will buy it; shizuka nara ii desu, if it is quiet, that is fine. You will also hear the tara conditional built on the past form, takakattara and shizuka dattara, which is more casual and often interchangeable.

The ii and yoi exception

There is exactly one irregular adjective, and it is one of the most common words in the language. Ii, good, is the shortened modern form of yoi. The shortening only happened in the plain present, so ii desu and ii hon are normal, but every other form goes back to yoi: yokatta, yokunai, yokunakatta, yokute, yoku, yokereba. Ikatta and ikunai do not exist.

This spreads to compounds. Kakko ii, cool or good-looking, becomes kakko yokatta and kakko yokunai. Atama ga ii, clever, becomes atama ga yokunai. Yoku on its own is also an extremely common adverb meaning well or often: yoku dekimashita, well done; yoku ikimasu, I often go.

Yokatta deserves special mention because it is a whole expression: said on its own it means what a relief, or I am glad. Yokatta desu ne is how you share someone's good news.

A speaking drill routine

Charts are for reference; speech comes from repetition. The routine below takes about ten minutes and works best out loud, standing up, at a steady pace. The goal is not to think about the ending but to feel it arrive.

• Pick five i-adjectives and five na-adjectives you use often, for example takai, oishii, samui, isogashii, ii and shizuka, genki, benri, kirei, taihen
• Chant each one through the plain column: takai, takakunai, takakatta, takakunakatta, without pausing
• Repeat the column in polite form, adding desu to each i-adjective form and swapping the copula for the na-adjectives
• Answer quick questions about yesterday in the past tense: samukatta? isogashikatta? tanoshikatta? and reply with a full sentence each time
• Join pairs with the te form: yasukute oishii, shizuka de kirei, atarashikute benri
• Make three sentences with ku naru or ni naru about changes you noticed this week
• Finish with ii in every form: ii, yokunai, yokatta, yokunakatta, yokute, yoku, yokereba

Do this for a week and the endings will start turning up in real conversation on their own. Record one run on your phone and listen for the place where you hesitate; that is the form to drill tomorrow.

Common mistakes and how to fix them

Almost every learner makes the same handful of mistakes, and they are all fixable with the chart. The list below gives the wrong form, the right form and the reason.

• Takai deshita for it was expensive: the past goes inside the adjective, takakatta desu
• Takai ja nai for it is not expensive: i-adjectives take kunai, so takakunai; ja nai is only for na-adjectives and nouns
• Kirekatta or kirei kunai for kirei: it is a na-adjective, so kirei datta and kirei ja nai
• Ikatta or ikunai for ii: the stem is yoi, so yokatta and yokunai
• Shizuka kute for quiet and: na-adjectives use de, so shizuka de
• Oishii ni taberu for eat deliciously: i-adjectives take ku, so oishiku taberu
• Genki ni desu or benri ni desu: the ni form is an adverb and cannot end a sentence with desu
• Putting both past markers on: takakatta deshita is doubled, takakatta desu is right

If you catch yourself mid-sentence, simply restart the adjective: sumimasen, takakatta desu. Native speakers do exactly this and nobody minds. What matters is that the corrected form is the one that comes out.