Japanese adjectives or 形容詞 (keiyoushi) are basically used as predicates and noun modifiers. They are divided into 2 groups: い-adjectives (i-adjectives) and な-adjectives (na-adjectives).
い-adjectives are adjectives ending with い while な-adjectives are mostly adjectives that end without い.
But there are exceptions of な-adjectives which end with い. I will come back to that later. Or you can click here to check these exceptions.
When Japanese adjectives are used as predicates, the simplest format is:
Noun は い-adjectives です
Noun wa i-adjective desu
Meaning: Noun is i-adjective
Noun は な-adjectives です
Noun wa na-adjective desu
Meaning: Noun is na-adjective
Note that です at the end of the sentence shows that the speaker is polite to the listener. So let us use some examples to express the above sentence format:
To change an い-adjective to its negative form, remove the "い" at the end of the adjective and replace it with "くない":
い)です → い-adj(～くない)です
Another way to express the negative form of an adjective is to replace the "い" with "くありません":
い)です → い-adj(～くありません)
As "～くありません" itself is already in polite form, the "です" at the end of the sentence is not required. Applying negative form to the previous い-adjective example:
To change a な-adjective to negative form, replace the "です" with "ではありません" at the end of the sentence:
な-adjです → な-adjではありません
Applying negative form to the previous な-adjective example:
Japanese adjectives are also used as noun modifiers. To modify a noun in a sentence, simply place an adjective before the noun to modify it. However, for な-adjectives, you need to add an additional "な" before the noun:
Topic は い-adjectives Noun です
Topic wa i-adjective Noun desu
Meaning: Topic is an i-adjective Noun
Topic は な-adjectives な Noun です
Topic wa na-adjective na Noun desu
Meaning: Topic is a na-adjective Noun
Using the same examples:
Most of the time beginners tend to forget to add the "な" when making a noun modifier sentence. So please take some effort to remember this.
In summary, you can form sentences with Japanese adjectives using either ways such as:
For the moment, I will show you 3 な-adjectives that end with "い":
Therefore, when used as noun modifier, don't forget to add a "な" before the noun:
Not to forget the negative forms for these 3 な-adjectives:
There is one い-adjective that you need to take note of when changing it to its negative form. For いい (ii) which means good, the negative form is よくない (yokunai), not いくない.
As you can see, there are many exceptions, not only in Japanese adjectives, but in the language as a whole. You will get to see more of them as you progress. Just pay attention, and you will be fine.