The te-form (て形) is one of the most frequently used verb forms in Japanese: 〜ている (ongoing action), 〜てください (please do...), 〜てから (after doing...) — they all need it.
But when godan verbs attach て or た, something called sound change (音便 / おんびん) happens. This is exclusive to godan verbs — ichidan and irregular verbs are unaffected.
Ichidan & Irregular Verbs: The Easy Part First
Before diving into sound changes, let's handle the simple cases.
Ichidan, ka-gyou (来る), and sa-gyou (する) verbs attach て/た with no sound changes — just use the 2nd form (drop る / use し / use き) and attach directly:
Drop る (ichidan) or change to the appropriate form (irregulars), then attach て or た. Completely regular, nothing to worry about.
Godan Sound Changes: Three Types
Godan verbs are a different story. When attaching て/た, the last kana undergoes one of three sound changes depending on what it is:
Conditions for Sound Change
| Condition | Details |
|---|---|
| Only godan verbs | Ichidan and irregulars are unaffected |
| Only when attaching て/た and related particles | てから, たり, ても, たら, etc. |
| Sound change type determined by the ending kana | Different endings → different changes |
Overview Table
| Ending | Sound change | て form | た form |
|---|---|---|---|
| く | イ音便 | いて | いた |
| ぐ | イ音便 | いで | いだ |
| う | 促音便 | って | った |
| つ | 促音便 | って | った |
| る | 促音便 | って | った |
| む | 拨音便 | んで | んだ |
| ぶ | 拨音便 | んで | んだ |
| ぬ | 拨音便 | んで | んだ |
| す | No change | して | した |
イ音便 (i-onbin): く and ぐ endings
Rule: く/ぐ becomes い, then attach て/た.
For ぐ endings, because of the voiced consonant, the following て/た also becomes voiced: で/だ.
く → いて, ぐ → いで. Remember: voiced ending (ぐ) gets voiced suffix (で).
促音便 (sokuon-bin): う, つ, and る endings
Rule: う/つ/る becomes the small っ (double consonant), then attach て/た.
| Verb | Ending | Change | て form | た form |
|---|---|---|---|---|
| 会う | う | う→っ | 会って | 会った |
| 待つ | つ | つ→っ | 待って | 待った |
| 降る | る | る→っ | 降って | 降った |
| 買う | う | う→っ | 買って | 買った |
| 立つ | つ | つ→っ | 立って | 立った |
| 送る | る | る→っ | 送って | 送った |
う/つ/る → って/った. The ending gets "swallowed" by the small っ.
拨音便 (hatsuon-bin): む, ぶ, and ぬ endings
Rule: む/ぶ/ぬ becomes the nasal ん, then attach て/た.
Because of the nasal sound, the following て/た also becomes voiced: で/だ.
む/ぶ/ぬ → んで/んだ. Nasal (ん) triggers voiced suffix (で) — same principle as ぐ in イ音便.
No Sound Change: す endings
す-ending godan verbs undergo no sound change. Just use the 2nd form (し) and attach て/た directly.
す is the only godan ending that doesn't trigger a sound change.
The One Exception: 行く
行く (いく, "to go") is the sole exception in all of godan sound change rules.
By the rules, く endings should use イ音便: 行く → 行いて. But 行いて sounds awkward, so Japanese speakers switched it to 促音便 instead:
Only 行く breaks the rule. Every other く-ending verb (書く → 書いて, 歩く → 歩いて) follows イ音便 normally. This is a guaranteed test question.
Memory Aid
Group the nine endings into three sets:
| Mnemonic | Endings | Change |
|---|---|---|
| い eats く/ぐ | く→いて, ぐ→いで | イ音便 |
| っ eats う/つ/る | う/つ/る→って | 促音便 |
| ん eats む/ぶ/ぬ | む/ぶ/ぬ→んで | 拨音便 |
| す stays clean | す→して | No change |
Voicing rule: ぐ, む, ぶ, ぬ — when the ending has voicing or is nasal, the て/た becomes で/だ.
Complete Reference Table
| Verb | Type | て form | た form |
|---|---|---|---|
| 書く | イ音便 | 書いて | 書いた |
| 急ぐ | イ音便 | 急いで | 急いだ |
| 会う | 促音便 | 会って | 会った |
| 待つ | 促音便 | 待って | 待った |
| 降る | 促音便 | 降って | 降った |
| 読む | 拨音便 | 読んで | 読んだ |
| 遊ぶ | 拨音便 | 遊んで | 遊んだ |
| 死ぬ | 拨音便 | 死んで | 死んだ |
| 話す | No change | 話して | 話した |
| 行く | Exception | 行って | 行った |
| 食べる | Ichidan | 食べて | 食べた |
| 来る | Ka-gyou | きて | きた |
| する | Sa-gyou | して | した |
Summary
- Sound changes only affect godan verbs attaching て/た (and related particles like ても, たら, たり)
- Three types: イ音便 (く/ぐ→い), 促音便 (う/つ/る→っ), 拨音便 (む/ぶ/ぬ→ん)
- す endings have no sound change — just use し + て/た
- Voiced/nasal endings (ぐ, む, ぶ, ぬ) trigger voiced suffixes で/だ
- 行く is the only exception: uses 促音便 (行って) instead of イ音便
- Ichidan and irregular verbs never undergo sound changes
Practice Questions
Q1. Write the て form of 泳ぐ.
Show answer
泳いで
泳ぐ ends in ぐ → イ音便: ぐ becomes い. Since ぐ is voiced, the suffix is で (not て).
Q2. What is the た form of 飲む?
Show answer
飲んだ
飲む ends in む → 拨音便: む becomes ん. Nasal sound triggers voiced suffix だ (not た).
Q3. Why is the て form of 行く written as 行って instead of 行いて?
Show answer
行く is the only exception in godan sound change rules. Although く endings normally use イ音便 (producing 行いて), the pronunciation felt unnatural, so Japanese adopted 促音便 instead: 行って. Only 行く does this — all other く-ending verbs (e.g., 書く → 書いて) follow イ音便 normally.