Master Class: Conjugating Japanese い-Adjectives (N5)

Welcome to your definitive guide to mastering い-adjectives (i-adjectives) in the negative and past tenses.

In Japanese, adjectives are incredibly dynamic. Unlike English adjectives, Japanese い-adjectives act almost like verbs—they conjugate directly to show tense (present/past) and polarity (affirmative/negative).

By the end of this guide, you will confidently transform words like samui (cold) into "was not cold" (samukunakatta). Let’s dive in!

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The Golden Rule: Drop the ~い (i)

To conjugate any い-adjective, your starting step is always the same: Drop the final ~い and attach the correct suffix.

Here is your master conjugation matrix using 暑い (あつい - atsui / hot):暑

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Step-by-Step Conjugation breakdown

1. Present Negative: ~くない (kunai)

To say something is not [adjective], drop the final い and add くない.

• Example: 寒い (samui / cold) $\rightarrow$ 寒くない (samukunai / not cold)寒
• Polite: 寒くないです (samukunai desu)寒

2. Past Affirmative: ~かった (katta)

To say something was [adjective], drop the final い and add かった.

• Common Mistake: Do not say samui deshita. You must conjugate the adjective itself!
• Example: 寒い (samui) $\rightarrow$ 寒かった (samukatta / was cold)寒
• Polite: かったです (samukatta desu)

3. Past Negative: ~くなかった (kunakatta)

To say something was not [adjective], drop the final い and add くなかった.

• Pro Tip: Think of this as taking the negative form (~くない), dropping the final い, and adding かった (~くなく + かった).
• Example: 寒い (samui) $\rightarrow$ 寒くなかった (samukunakatta / was not cold)寒
• Polite: 寒くなかったです (samukunakatta desu)寒

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⚠️ The Crucial Exception: いい (ii / Good)

The word for "good" is いい (ii) or 良い (yoi).
When conjugating this adjective, you must use the stem よ (yo). You cannot conjugate ii directly.良

• Good: いい / よい (ii / yoi)
• Not good: よくない (yokunai)
• Was good: よかった (yokatta)
• Was not good: よくなかった (yokunakatta)

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Quick Challenge!

Test your skills. Try to conjugate the adjective 安い (やすい - yasui / cheap) into the following forms. (Scroll down for answers!)安

1. It is not cheap (Polite)
2. It was cheap (Casual)
3. It was not cheap (Polite)

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Answers:

1. 安くないです (yasukunai desu)安
2. 安かった (yasukatta)安
3. 安くなかったです (yasukunakatta desu)安

Contextual Examples

Let's look at how these look in real N5-level sentences.

1. Present Negative (Polite):

   • このお茶は熱くないです。茶熱
   • Kono ocha wa atsukunai desu.
   • This tea is not hot.
   茶熱

2. Past Affirmative (Polite):

   • 昨日のテストは難しかったです。昨日難
   • Kinou no tesuto wa muzukashikatta desu.
   • Yesterday's test was difficult.
   昨日難

3. Past Negative (Casual):

   • 映画はあまり面白くなかった。映画面白
   • Eiga wa amari omoshirokunatta.
   • The movie wasn't very interesting.
   映画面白

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