I-Adjectives (い形容詞)
Master Japanese Descriptive Words and Their Conjugations
Table of Contents
1. What are I-Adjectives?
I-adjectives (い形容詞) are Japanese adjectives that end in い
They conjugate like verbs and can stand alone as predicates
Understanding I-Adjectives
Independent Nature: Can function as complete predicates without です
Verb-like Conjugation: Change endings for tense and polarity
Descriptive Power: Express qualities, emotions, and characteristics
Flexible Positioning: Can modify nouns directly or stand as predicates
Essential Vocabulary: Among the most frequently used words in Japanese
2. How to Recognize I-Adjectives
Recognition Patterns
Ending Pattern
All true I-adjectives end with い sound
Examples
Ends in い, modifies nouns directly
False Friends
Ends in い but is actually na-adjective!
I-Adjective vs Na-Adjective Recognition
| Type | Pattern | Example | Before Nouns |
|---|---|---|---|
| True I-Adjective | Ends in い (conjugates) | 高い (takai) | 高い車 (takai kuruma) |
| Na-Adjective ending in い | Ends in い (no conjugation) | きれい (kirei) | きれいな車 (kirei na kuruma) |
| Typical Na-Adjective | Various endings | 静か (shizuka) | 静かな車 (shizuka na kuruma) |
3. Basic Usage & Structure
Two Main Functions
Pattern: I-adj + Noun
Pattern: Noun は I-adj
Sentence Structures
Simple Predicate:
この本は面白い。
Polite Form:
この本は面白いです。
Noun Modification:
面白い本を読みます。
4. Conjugation Patterns
Basic Conjugation Rules
| Form | Pattern | Example (高い) | Reading | English |
|---|---|---|---|---|
| Dictionary Form | ___い | 高い | takai | expensive/high |
| Polite Present | ___いです | 高いです | takai desu | is expensive (polite) |
| Past | ___かった | 高かった | takakatta | was expensive |
| Polite Past | ___かったです | 高かったです | takakatta desu | was expensive (polite) |
| Negative | ___くない | 高くない | takakunai | not expensive |
| Past Negative | ___くなかった | 高くなかった | takakunakatta | was not expensive |
Step-by-Step Conjugation
Starting with 面白い (omoshiroi – interesting):
1. Remove い: 面白い → 面白
2. Add new ending:
• Past: 面白 + かった = 面白かった
• Negative: 面白 + くない = 面白くない
• Past Negative: 面白 + くなかった = 面白くなかった
Exception – いい/良い (good):
• いい → よかった (not いかった)
• いい → よくない (not いくない)
5. Most Common I-Adjectives
Essential Daily Adjectives
Opposite: 小さい (chiisai)
Opposite: 安い (yasui)
Opposite: 古い (furui)
Opposite: つまらない (tsumaranai)
Opposite: 悪い (warui)
Opposite: 暇 (hima – na-adj)
Complete Common I-Adjectives List
| Kanji | Hiragana | Romaji | English | Category |
|---|---|---|---|---|
| 長い | ながい | nagai | long | Size/Shape |
| 短い | みじかい | mijikai | short | Size/Shape |
| 広い | ひろい | hiroi | wide/spacious | Size/Shape |
| 狭い | せまい | semai | narrow | Size/Shape |
| 重い | おもい | omoi | heavy | Physical |
| 軽い | かるい | karui | light | Physical |
| 熱い | あつい | atsui | hot | Temperature |
| 冷たい | つめたい | tsumetai | cold (touch) | Temperature |
| 寒い | さむい | samui | cold (weather) | Temperature |
| 暑い | あつい | atsui | hot (weather) | Temperature |
| 美味しい | おいしい | oishii | delicious | Taste |
| まずい | まずい | mazui | bad taste | Taste |
| 甘い | あまい | amai | sweet | Taste |
| 辛い | からい | karai | spicy | Taste |
| 難しい | むずかしい | muzukashii | difficult | Quality |
| 易しい | やさしい | yasashii | easy/kind | Quality |
| 楽しい | たのしい | tanoshii | enjoyable | Emotion |
| 悲しい | かなしい | kanashii | sad | Emotion |
| 嬉しい | うれしい | ureshii | happy | Emotion |
| 眠い | ねむい | nemui | sleepy | State |
6. Past, Present & Negative Forms
Complete Conjugation Examples
| Base | Present | Past | Negative | Past Negative |
|---|---|---|---|---|
| 大きい | 大きい 大きいです | 大きかった 大きかったです | 大きくない 大きくないです | 大きくなかった 大きくなかったです |
| 面白い | 面白い 面白いです | 面白かった 面白かったです | 面白くない 面白くないです | 面白くなかった 面白くなかったです |
| いい/良い | いい いいです | よかった よかったです | よくない よくないです | よくなかった よくなかったです |
Practical Tense Usage
Present Situations:
今日は寒いです。
Past Experiences:
昨日の映画は面白かったです。
Negative Descriptions:
この問題は難しくないです。
7. I-Adjectives vs Na-Adjectives
Key Differences
| Aspect | I-Adjectives | Na-Adjectives |
|---|---|---|
| Ending | Always end in い | Various endings, some end in い |
| Before Nouns | 大きい車 (direct) | きれいな車 (need な) |
| As Predicate | 車は大きい (standalone) | 車はきれいだ (need だ/である) |
| Polite Form | 大きいです | きれいです |
| Past Form | 大きかった | きれいだった |
| Negative | 大きくない | きれいじゃない |
Common Confusion Points
きれい (beautiful): Ends in い but is na-adjective → きれいな人
嫌い (dislike): Can be both i-adj and na-adj depending on usage
有名 (famous): Written as ゆうめい, na-adjective → 有名な人
大好き (love): だいすき, na-adjective → 大好きな食べ物
8. Making Adverbs from I-Adjectives
Adverbial Form Pattern
Formation Rule
Describes HOW an action is done
Example
速く走る (run quickly)
Common Adverbial Forms
| I-Adjective | Reading | Adverb Form | Reading | English |
|---|---|---|---|---|
| 早い | はやい | 早く | はやく | early/quickly |
| 遅い | おそい | 遅く | おそく | late/slowly |
| 大きい | おおきい | 大きく | おおきく | largely |
| 小さい | ちいさい | 小さく | ちいさく | small-ly |
| よい/いい | よい/いい | よく | よく | well |
| 悪い | わるい | 悪く | わるく | badly |
Adverb Usage Examples
Describing Actions:
日本語を上手く話します。
Time Expressions:
早く来てください。
9. Degrees of Comparison
Expressing Intensity
Very (とても)
Most common intensifier
Really (本当に)
Emphasizes truth/reality
Extremely (すごく)
Casual, strong emphasis
Comparison Patterns
| Type | Pattern | Example | Translation |
|---|---|---|---|
| More than | A は B より I-adj | 車は自転車より速い | Cars are faster than bicycles |
| Most | A が一番 I-adj | この本が一番面白い | This book is the most interesting |
| As…as | A は B と同じくらい I-adj | 今日は昨日と同じくらい寒い | Today is as cold as yesterday |
Comparison in Context
東京は大阪より大きいです。
10. Practice & Applications
Daily Description Practice
Weather & Temperature:
今日は暖かくて、昨日は寒かったです。
Food & Taste:
このケーキは甘くて美味しいです。
Emotions & States:
試験の後、嬉しくて楽しかったです。
Practical Application Exercises
| Exercise Type | Task | Example | Goal |
|---|---|---|---|
| Daily description | Describe your day using 5 i-adjectives | 今日は忙しくて疲れました | Natural expression |
| Food reviews | Describe meals with taste adjectives | ラーメンは辛くて美味しい | Practical vocabulary |
| Comparisons | Compare two items using より | 夏は冬より暑い | Comparative structures |
| Past experiences | Talk about past events with past tense | 旅行は楽しかった | Tense accuracy |
Mastery Checklist
Beginner Level: Recognize and use 20 basic i-adjectives in present tense
Intermediate Level: Master all tense forms and use adjectives to modify nouns
Advanced Level: Use adverbial forms and complex comparisons naturally
Expert Level: Combine multiple adjectives and express subtle nuances
Common Mistake Prevention
Don’t confuse: 熱い (hot to touch) vs 暑い (hot weather)
Remember: いい becomes よかった in past tense, not いかった
Watch out: Some い-ending words are na-adjectives (きれい, 有名, etc.)
Practice: Adverb forms (い→く) vs te-forms for connecting adjectives
I-Adjective Mastery Achieved!
You now understand the fundamental building blocks of Japanese description! I-adjectives are essential for expressing your thoughts, feelings, and observations about the world around you.
I-Adjectives Quiz
Test Your Knowledge of Japanese I-Adjectives (い形容詞)
Exercise 1: Basic Recognition
What is the Japanese term for I-adjectives?
Explanation: I-adjectives are called い形容詞 because they end in い and conjugate independently.
Exercise 2: Adjective Recognition
Which of these is a true I-adjective?
Explanation: 大きい is a true I-adjective. きれい ends in い but is a na-adjective, and 有名 is also a na-adjective.
Exercise 3: Past Tense Conjugation
What is the past tense of 高い (takai)?
Explanation: I-adjectives form past tense by changing い to かった.
Exercise 4: Negative Form
What is the negative form of 面白い (omoshiroi)?
Explanation: I-adjectives form negative by changing い to くない.
Exercise 5: Special Case
What is the correct past tense of いい (ii)?
Explanation: いい is irregular – it uses よ- stem for all conjugations except the dictionary form.
Exercise 6: Adverbial Form
How do you make an adverb from 速い (hayai)?
Explanation: I-adjectives form adverbs by changing い to く.
Exercise 7: Temperature Adjectives
Which adjective describes hot weather?
Explanation: 暑い describes hot weather/atmosphere, while 熱い describes hot temperature to touch.
Exercise 8: Usage Pattern
How do I-adjectives modify nouns?
Explanation: I-adjectives modify nouns directly without な or other particles.
Exercise 9: Comparison
How do you say “more expensive than”?
Explanation: Use より + I-adjective for “more [adjective] than” comparisons.
Exercise 10: Past Negative
What is the past negative form of 美味しい (oishii)?
Explanation: Past negative: い → くなかった (美味しい → 美味しくなかった)
Exercise 11: Emotion Adjectives
Which means “sad”?
Explanation: 悲しい means sad. 嬉しい means happy, and 楽しい means fun/enjoyable.
Exercise 12: Polite Form
How do you make 寒い (samui) polite?
Explanation: I-adjectives become polite by adding です after the adjective.
Exercise 13: Size Adjectives
What is the opposite of 大きい (ookii)?
Explanation: 小さい means small and is the opposite of 大きい (big).
Exercise 14: Connecting Adjectives
How do you connect “expensive and good”?
Explanation: Connect I-adjectives using て-form: い → くて.
Exercise 15: Practical Usage
How do you say “This book was interesting”?
Explanation: Past polite form: 面白い → 面白かった → 面白かったです
Exercise 16: Taste Adjectives
Which adjective means “spicy”?
Explanation: 辛い means spicy. 甘い means sweet, and 酸っぱい means sour.
Exercise 17: False Friends
Which word ending in い is NOT an I-adjective?
Explanation: 嫌い functions as a na-adjective when used attributively: 嫌いな食べ物
Exercise 18: Superlative
How do you say “the most interesting”?
Explanation: 一番 + adjective expresses superlative “most [adjective]”.
Exercise 19: Condition Adjectives
Which means “busy”?
Explanation: 忙しい means busy. 疲れた means tired, and 眠い means sleepy.
Exercise 20: Advanced Usage
Complete the sentence: この映画は面白く___。
Explanation: 面白くありません is a more formal way to say “not interesting” than 面白くない.
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