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Understanding Japanese Adjective Conjugation

In language, there are ways to express things very simply and ways to express things in a more nuanced way.   When expressing ideas and opinions, it becomes important to be able to modify nouns and verbs. These modifying words are called adjectives and adverbs.  


It’s important to know that in Japanese, descriptions pretty much always go in front of what they are describing.


This is true for adjectives as well. This should be at least a little familiar to native English speakers, as the adjective tends to go in front of the noun it describes.   There are effectively two types of Japanese adjectives, -na adjectives and -i adjectives. Further, Japanese heavily relies on conjugation, which makes it more uniform than English. Japanese adjectives are no exception to the conjugation that Japanese has. We will expand upon these topics and more below.  


Normal Adjective Usage

In order to grasp the conjugations of Japanese adjectives, it’s important to first realize the normal ways that adjectives are used.  


Adjectives are words that describe a noun. For instance, if I were to say, “The quick fox”, then the word “quick” is the adjective that describes the noun, “fox”. In English, the adjective tends to come before the noun it describes, which is the opposite of, say, how Spanish adjectives are used.


Luckily for English speakers, Japanese adjectives usually come before the noun it describes. For instance, in 酷い仕打ち (hidoi shiuchi, cruel treatment), the adjective 酷い (hidoi, cruel) describes the noun 仕打ち (shiuchi, treatment). Similarly, consider 温かい御飯 (atatakai gohan, warm rice) has the adjective 温かい (atatakai, warm) come before and describe the noun 御飯 (gohan, rice).  


Have you noticed a pattern? The adjectives mentioned above all end in い (i). That is because those are most common. As mentioned earlier, there are effectively two types of Japanese adjectives, -i adjectives and -na adjectives. As you can probably guess, the -i adjectives end in い (i), while -na adjectives end in な (na).  


Here’s another example. 綺麗な景色 (kirei na keshiki, pretty view) has the adjective 綺麗 (kirei, pretty), which describes the noun 景色 (keshiki, view). The word 綺麗 (kirei, pretty) is often written in kana, like キレイ (kirei) or きれい (kirei), but I want to make it clear that it is a -na adjective and not an -i adjective. Notice how the kanji ends with the -i and that it does not, when written with kanji, end with い (i).   


Though they are effectively adjectives, many may consider -na adjectives to be nouns, and they are conjugated like nouns, not like normal -i adjectives. -na adjectives are essentially treated like a noun in such grammatical cases, except you can modify nouns with them by putting な (na) at the end.  


While still on the topic of -na adjectives, some -i adjectives actually can also be -na adjectives. For instance, 小さい (chiisai, small) can become a -na adjective by removing the い (i) and adding な (na). It then becomes 小さな (chiisana, small). Notice that this is more of a rarity than something you can do to most adjectives, as you can only do it to relatively few -i adjectives. With that out of the way, let’s get to conjugating!  


Japanese grammar guide  

Simple Conjugations

Normal -i adjectives can become adverbs by removing the い (i) and adding く (ku). So, 手早い (tebayai) as an adjective means nimble or quick. As an adverb, however, 手早く (tebayaku) means nimbly or quickly, such as in 手早く稼ぐ (tebayaku kesagu) means to labor nimbly.  


This can work with pretty much all -i adjectives to turn to them into adverbs. But this form is important not only to change adjectives into adverbs, but also to a lot of other conjugations with adjectives. For instance, if you wanted to use the negative form of the adjectives, then you’d change it to the adverb form and then add ない (nai).  


For example, take the adjective 寒い (samui, cold) and make it negative by dropping the い (i), adding く (ku), and then adding ない (nai) to become 寒くない (samukunai, not cold). The ない (nai) part itself works as an adjective, so the word is still an adjective. If you want to use the negative form of an adjective as an adverb, you simply drop the い (i) and add a く (ku), just like you’d normally do.  


So, as an adverb, 寒くない (samukunai) would become 寒くなく (samukunaku). 怖い (kowai, frightening), if you wanted the negative form, would become 怖くない (kowakunai, not frightened). And so it is for most -i adjectives.   To talk of the past tense, you drop the い (i) and add かった (katta) on an -i adjective. So, 辛い (karai, spicy) would become 辛かった (karakatta) to mean that whatever it is describing was spicy.  


Remember how I said the ない (nai) part of a negative adjective itself acts like an adjective? Knowing this, can you guess how you’d make the negative past tense form of an adjective? You simply take the negative form of an adjective and then make it past tense. For example, 暑い (atsui, hot or warm) would become 暑くない (atsukunai) to become the negative form. Then, to become the negative past form of the verb, 暑くない (atsukunai) would become 暑くなかった (atsukunakatta), which means it wasn’t hot. Similarly, 優しい (yasashii, kind), would become 優しくなかった (yasashikunakatta, wasn’t kind).  


Other Conjugations

Now that some of those basic conjugations are covered, we’re going to quickly go over some other popular conjugations of -i adjectives. You can take an -i adjective and make it a noun by removing the い and adding さ (sa).   So, 懐かしい (natsukashii, nostalgic) can become 懐かしさ (natsukashisa) to mean nostalgia. You can also drop the い (i) of an -i adjective and add そう (sou) to describe how something or someone seems. So, 厳しい (kibishii, strict) becomes 厳しそう (kibishisou) to mean that something or someone seems strict.


Alright, we have one last conjugation to go over. That is how you can drop the い (i) of an -i adjective and add すぎる (sugiru) to mean that the adjective becomes too much of what said adjective means. It is easier to think of it as meaning “too [insert adjective]”.


That may be confusing, so let me provide an example. If you say someone is 弱い (yowai, weak), then saying that he or she is 弱すぎる (yowasugiru) would mean that said someone is too weak. The すぎる (sugiru) part would then conjugate like a special -ru verb, but that is a different topic.  


Learn Japanese adverbs in context

Adjectives are an important part of language, and so it is also important to know how to use them and conjugate them well. Rather than study each one individually, why not learn them in context? This way, you also learn how to conjugate them as well.  


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