Basics of Japanese Adjective Conjugation

Many learners need help to get used to Japanese adjective conjugation. Let’s review the basic rules and cement your knowledge.

Why do adjectives conjugate? Is it necessary?

Yes. Adjective conjugation is one of the most important aspects of Japanese grammar. Conjugated adjectives are necessary to express negation, tense, conditional, etc.

Here are 7 conjugation patterns of adjectives. 

-Attribute form

-Infinitive form

-Negative form

-Adverb form

-Conjunctive form (Te-form)

-Past form (Ta-form)

-Conditional form (Ba-form)

There are 2 kinds of adjectives in Japanese: い-adjectives and な-adjectives. So why are there 2 kinds? This is because な-adjectives were invented later than い-adjectives. During the Heian period (795-1185), there were not enough adjectives to describe complex concepts. So they converted some nouns into adjectives by adding な at the end. This is how な-adjectives were made. Therefore, い-adjectives often describe fundamental concepts such as emotions, sensations, and colors, while な-adjectives tend to describe abstract concepts such as states of things.

い-adjectives end with い, and な-adjectives end with な. See the following adjectives. Can you guess which is which?

The answer is, あつい, たのしい, and かわいい are い-adjectives, and きれいな, にぎやかな, and べんりな are な-adjectives. Easy! Both types of adjectives are used in the same way in sentences. The only difference is the pattern of conjugation.

In summary, Japanese adjectives have 7 conjugation forms, and each of the 2 adjective types has its conjugation pattern. Therefore, you must know at least 14 patterns to use an adjective correctly. Let's look at them one at a time!

Attribute form

Any adjectives ending with い or な are in the attribute form. The attribute form of an adjective is a basic form used to describe nouns. You can put them directly before nouns, just like English adjectives.

And you need to remember the attribute forms to know the stem of an adjective. 

The stem is a fixed part that is not affected by conjugation. In this example, かわい and にぎやか are the stems. Conjugation changes the parts in red: the last い and な in the attribute form. 

Infinitive form

The infinitive form is used when an adjective is at the end of a sentence.

For the infinitive form, い-adjectives are the same as the attribute form, while な-adjectives change to “stem+だ”. This だ is a short form of です. だ/です are auxiliary verbs that are used at the end of assertive sentences. Assertive sentences are sentences like “X is Y” and their endings are always nouns or adjectives. です is politer than だ and more common in polite conversation.

Negative form

When the sentence is negative, you must change the adjective to negative form.

For the negative form, い-adjectives change to “stem+くない”, and な-adjectives change to “stem+じゃない”. If you say かわいいじゃない/にぎやかくない, it’s wrong because かわいい is an い-adjective and にぎやかな is a な-adjective. Please do not mix up these 2 conjugation patterns. 

The negative form can be used in front of nouns just like the attribute form.

And of course, when it’s the last word of a sentence, you can add です at the end to make the sentence more polite.

Adverb form

You can turn adjectives into adverbs using the adverb form. Adverbs are content words to describe verbs or adjectives. For example, “slow” is an adjective, and “slowly” is an adverb. Here are the adverb forms:

For the adverb form, い-adjectives change to “stem+く”, and な-adjectives change to “stem+に”. Japanese grammatical order is Subject+Object+Verb, while English is SVO. So verbs are always at the end of sentences. Adverbs are usually right before verbs. 

Conjugative form (Te-form)

When you list 2 or more adjectives in one sentence, you must change the adjectives into the conjugative form except the last one. Let’s look at an example.

There are 3 adjectives in this sentence; かわいい, にぎやかな, たのしい. The first and second adjectives must be in the conjunctive forms to connect to the next adjective. For the conjunctive form, い-adjectives change to “stem+くて” and な-adjectives change to “stem+で”. The conjugative forms cannot be used at the end of sentences.

Past form (Ta-form)

The past form expresses the past tense.

For the past form, い-adjectives change to “stem+かった”, and な-adjectives change to “stem+だった”. Like other forms, the past form can be put in front of nouns, too.

Can you add です at the end to the past form when it’s at the end of a sentence? Yes and no. Look at the examples.

For い-adjectives, you can add です after the past form. However, for な-adjectives, “stem+だった” changes to “stem+でした” when it’s polite. This is because だった is a short form of でした. Do not mix up these rules. かわいかったでした/にぎやかだったです are incorrect.

Conditional form (Ba-form)

The conditional form expresses conditions. It’s the part of the sentence that contains “if” in sentences such as: “If it’s sunny tomorrow, I will go outside.”

For the conditional form, い-adjectives change to “stem+ければ” and な-adjectives change to “stem+ならば/であれば”.

The past form +ら also works as the conditional form.

Here is a summary.

So, how can you change the conjugative form, the past form, and the conditional form to the negative? What are the differences among the several conditional forms? Take a Japanese lesson to find out the answer!