治する

Different conjugations of the verb in both plain form and keigo (polite)

Verb conjugations

Each form has a small speaker icon next to it — click it to hear the pronunciation read aloud.

Plain form vs keigo

Plain form is the basic form of a verb or adjective in Japanese. It's called "plain" because it's the simplest and most straightforward form, without any added politeness or formality. Plain form is used in informal situations, such as talking to friends, family, or people of lower status.

Keigo, on the other hand, is a set of honorific language expressions used to show respect, politeness, and formality in Japanese.

In general, plain form is used in informal situations and keigo is used in formal situations. However, it's important to note that there are different levels of keigo depending on the level of formality and the relationship between the speaker and listener. For example, the keigo used with a superior in a workplace setting might be different from the keigo used with a customer or client.

It's also worth noting that keigo can be difficult to master, even for native Japanese speakers. There are many different honorific expressions and rules for using them correctly, so it's important to study and practice them carefully in order to use them effectively.

Not every form above has a distinct keigo equivalent: the conditional, provisional conditional, causative, and potential forms aren't typically expressed differently in polite speech, so only forms with their own recognized keigo pattern are shown in the Keigo column.

Some Japanese verbs are formed by attaching する ("to do") to a noun or a bound kanji, for example 恋する ("to fall in love") or 愛する ("to love").

Dictionaries (including this one) tag these verbs to describe how they're built. You can see the full list of tags used on this site for parts of speech on the Parts of Speech page, but the two relevant here are:

• vs-i ("suru verb – included"): a free noun or morpheme plus する.
• vs-s ("suru verb – special class"): a single bound kanji plus する.

Verbs tagged vs-i always conjugate exactly like する itself:

• Negative: しない
• Potential: できる
• Imperative: しろ
• Volitional: しよう

Verbs tagged vs-s, like 愛する, 達する, or 反する, sometimes use a different pattern for these same four forms instead:

For example, 愛する ("to love") uses the alternate pattern: its negative form is 愛さない, not 愛しない.

Which pattern a given vs-s verb actually uses isn't predictable from its tag alone. Dictionaries and native speakers don't always agree, and usage is still shifting for many of these words. We only show the alternate pattern for verbs we've individually confirmed use it. For every other vs-s verb, we show the standard する pattern as the most likely default, but it hasn't been individually verified for that specific word, and the alternate pattern may be the one you'll actually encounter in practice.

If you know for certain which pattern is correct for a verb showing this notice, please contact us so we can verify it and update the site.