Japanese Verb Stems: How Japanese Verb Conjugation Works

When you're learning Japanese, you'll eventually hit a point where you realize that verbs are kind of the backbone of the whole language. So what is a Japanese verb stem, exactly? The verb stem (or , ren'youkei in traditional Japanese grammar) is basically the base form you get when you strip away certain endings from a verb. This stem becomes the foundation for tons of other conjugations you'll use constantly. Let me walk you through the basics!

Why verb stems matter for Japanese grammar

The verb stem plays a huge role in verb conjugation. Seriously, once you know how to form stems correctly, you can create all sorts of expressions. Want to say you want to do something? Add たい (tai) to the stem. Want to suggest doing something together? Add ましょう (mashou). Want to make compound verbs? You'll use stems for that too.

I remember when I first started learning Japanese from a textbook, they just threw conjugation tables at me without really explaining why stems mattered. It felt like memorizing random patterns. But once I understood that the stem was this consistent base I could build on, everything made way more sense.

The three verb groups you need to know

Before we dive into forming stems, you need to understand that Japanese verbs fall into three groups. This matters because each group forms its stem differently.

Ichidan verbs (Group 2)

Ichidan verbs, also called る (ru) verbs, are the easiest to work with. These verbs end in either える (eru) or いる (iru). To form the stem, you literally just drop the final る. That's it.

Examples:

The kanji stays the same, you just remove that final る character. Super straightforward.

Godan verbs (Group 1)

Godan verbs, sometimes called う (u) verbs, are trickier. These verbs end in various う-line sounds: う, く, ぐ, す, つ, ぬ, ぶ, む, or る. Yeah, る shows up here too, which confuses the hell out of beginners.

Despite that, る is on the う-line of the hiragana chart, so it makes sense that some る ending verbs could potentially be considered godan verbs, right? The Japanese language just loves keeping you on your toes.

For godan verbs, you change the final う-line vowel to an い-line vowel. Here's what that looks like:

The pattern here is consistent. You're moving from the う-line to the い-line on the hiragana chart. Once you memorize the chart (which you should do anyway if you're serious about learning Japanese), this becomes pretty automatic.

Irregular verbs

There are only two truly irregular verbs in Japanese: する (suru, to do) and (kuru, to come). Thank goodness there are only two, because they break all the rules.

For する, the stem is し (shi). For , the stem is (ki). You just have to memorize these. The good news is you'll use these verbs so frequently that you'll internalize them pretty quickly.

How to use verb stems

Knowing how to form stems is one thing, but understanding what you can do with them is where things get practical. Here are the main uses you'll encounter constantly.

Expressing desire with たい (Tai)

Add たい to any verb stem to say you want to do that action. This is super common in everyday conversation.

You can conjugate たい like an adjective too. (tabetakunai) means "don't want to eat," and (tabetakatta) means "wanted to eat."

Making suggestions with ましょう (Mashou)

Add ましょう to the stem to suggest doing something together, like "let's do X."

This is the polite form. There's also a casual version using the volitional form, but that uses a different conjugation pattern.

Creating the polite form with ます (Masu)

The masu form is probably the first verb conjugation you learned. You take the stem and add ます for present/future polite, ました (mashita) for past polite, or ません (masen) for negative polite.

Continuous and progressive forms

Add ながら (nagara) to a stem to express doing two actions simultaneously.

You can also use the stem with certain auxiliary verbs to create other continuous forms, though this gets into more advanced territory.

Compound verbs

This is where Japanese gets really interesting. You can combine verb stems with other verbs to create new meanings. These are called compound verbs, and they're everywhere in Japanese.

Native speakers create these combinations all the time. Understanding stems helps you decode them when you encounter new ones.

Nominalization

You can use verb stems as nouns in certain contexts. This turns the action into a thing.

Some of these nominalized forms are so common that they function as standalone nouns in the language.

Connecting stems to particles and adjectives

Verb stems also interact with particles in specific ways. The particle に (ni) can attach to certain verb stems to indicate purpose, like (kaimono ni iku, "go shopping"), where (kaimono) comes from the stem of (kau, to buy).

Some verb stems can function similarly to adjective stems when combined with certain suffixes. The suffix やすい (yasui, easy to) and にくい (nikui, hard to) attach directly to verb stems.

Understanding how stems work with these constructions expands your ability to express nuanced meanings.

The traditional grammar perspective

Now, in linguistics and Japanese grammar (as in , kokugo bunpou or traditional Japanese grammar), what a verb stem is may be different (or was that the verb root?).

Traditional Japanese grammar identifies six verb bases, and what we're calling the "verb stem" here is specifically the (ren'youkei), or continuative form.

The six traditional bases are:

For most learners, you don't need to memorize all these traditional names. Modern Japanese textbooks usually simplify things by focusing on the masu-stem () because that's what you'll use most frequently. But if you're reading more advanced grammar resources or studying for something like the JLPT, you might encounter these terms.

Common mistakes and tricky cases

Confusing ichidan and godan る verbs

This trips up everyone. Some verbs ending in る are ichidan (just drop the る), while others are godan (change る to り). How do you know which is which?

If a verb ends in える or いる, it's probably ichidan. But there are exceptions. Verbs like (kaeru, to return), (hashiru, to run), and (hairu, to enter) are godan despite ending in eru or iru sounds.

Forgetting vowel changes in godan verbs

Beginners often forget to change the vowel when forming godan stems. They might say instead of . Remember, that final character has to shift from the う-line to the い-line.

Irregular verb confusion

する and are irregular, but compound verbs using these are also irregular. So (benkyou suru, to study) has the stem (benkyou shi), and (motte kuru, to bring) has the stem (motte ki).

Practical application and practice

The best way to internalize verb stems is through actual use.

The ultimate fast track to master the stem form?

Encounter verbs in context, and actively identify their stems! This active processing helps way more than passive reading. Your brain starts recognizing the patterns automatically, and eventually you'll conjugate verbs without consciously thinking about the rules. Reading native content helps too. Manga, light novels, news articles, social media posts - they all use verb conjugations constantly.

Invest your time, and it will pay the best interest one day!