Suffix ~Au: The Secret to Expressing Mutual Connection

~au (~合う)

If you have been studying for the JLPT N3 or N2 levels, you’ve likely encountered a specific type of verb that feels a bit “crowded.” You know the ones—they start with a familiar action like Hanashimasu (to speak) or Tasukemasu (to help), but then they have this extra bit tacked onto the end: ~au (~合う).

At first glance, it might seem like just another grammatical hurdle to jump over. You might be thinking, “I already know how to say ‘together’ (issho ni), so why do I need this?” But as you dive deeper into the Japanese language, you realize that Japanese isn’t just about the facts; it’s about the relationships between people. The suffix ~au is the linguistic bridge that connects two people in a single action. It captures that beautiful moment where an action isn’t just one-way, but reciprocal.

Before diving into the grammar detail, here is the JLPT N3 complete guide: 
How to Pass JLPT N3: Complete Study Guide, Exam Format & Strategies

In this guide, we are going to break down everything you need to know about ~au. We’ll look at the rules, explore some real-life scenarios, and help you avoid the common pitfalls that trip up even the most dedicated students. By the end of this post, you’ll be able to use this grammar point to sound more natural, more empathetic, and much more like a native speaker.

Understanding the Core Concept of ~Au

The kanji used for this suffix is 合, which carries the meanings of “to fit,” “to match,” or “to come together.” When you attach this to the end of another verb, it transforms that verb into a reciprocal action. In English, we usually translate this as “each other” or “to one another.”

Think about the difference between these two sentences:

1. “I looked at him.” (One-way action)
2. “We looked at each other.” (Reciprocal action)

In Japanese, that second sentence is where ~au shines. It signifies that the action is flowing in both directions simultaneously. It turns a solitary act into a shared experience. This is vital in Japanese culture, where harmony (Wa) and mutual support are highly valued. Using ~au shows that you recognize the interaction taking place, rather than just the individual actions of two people.

The Basic Grammar Rule

The good news is that the construction of this grammar point is incredibly straightforward. It follows the standard pattern for combining verbs in Japanese. You take the Masu-stem of your primary verb and simply add ~au.

Verb (Masu-stem) + 合う (au)

Let’s look at a few quick transformations:

• Hanasu (to talk) → Hanashi + Au = Hanashiau (to talk with each other / discuss)
• Tasukeru (to help) → Tasuke + Au = Tasukeau (to help each other)
• Aisu (to love) → Ai + Au = Aiau (to love each other)

Once you have combined them, the new compound verb conjugates just like a regular Group 1 (U-verb) because it ends in “u.” For example, the past tense of Hanashiau is Hanashiatta, and the polite form is Hanashiaimasu.

Daily Life Examples of ~Au in Action

To truly grasp how this works, we need to move away from textbooks and into real conversations. Here are three common ways you will hear and use ~au in your daily life in Japan.

Discussing Problems with Friends

Imagine you and your roommate are having a disagreement about the housework. You don’t want to just shout your opinions; you want to reach a solution together. This is where Hanashiau comes in.

Japanese: 大事なことだから、二人でしっかり話し合いましょう。
Romaji: Daiji na koto dakara, futari de shikkari hanashiaimashou.
English: This is important, so let’s have a proper discussion (talk it out) together.

Notice how “talk” becomes “talk it out” or “discuss” when ~au is added. It implies a back-and-forth exchange where both parties are listening and contributing. If you just said “hanashimashou,” it sounds more like “let’s speak,” which is a bit vague. Hanashiau signals a productive, mutual conversation.

Supporting Each Other During Hard Times

If you are a student, you know how stressful exam seasons can be. You and your classmates might study together, share notes, and encourage one another. This mutual support is perfectly described by Tasukeau.

Japanese: 困った時は、お互いに助け合うことが大切です。
Romaji: Komatta toki wa, otagai ni tasukeau koto ga taisetsu desu.
English: When times are tough, it is important to help each other.

In this sentence, we often see the word otagai ni (mutually/each other) used alongside the ~au verb. While ~au already means “each other,” adding otagai ni emphasizes the partnership. It’s a very common pairing you’ll see on the JLPT.

Sharing a Moment of Connection

Sometimes, ~au is used for physical or non-verbal actions. Imagine you are walking down the street and you see someone you recognize. You both make eye contact and smile at the same time. This is Miseumau (showing each other) or more commonly Warau (laughing) becoming Waraiau.

Japanese: 久しぶりに会った友達と、顔を見合わせて笑い合った。
Romaji: Hisashiburi ni atta tomodachi to, kao o miawasete waraiatta.
English: I looked at my friend’s face whom I hadn’t seen in a long time, and we laughed together.

Here, Waraiau isn’t just “we laughed.” It implies that your laughter was triggered by each other—you were sharing the joy. It paints a much more vivid picture of the friendship than using the standard plural form of “to laugh.”

Nuances and Common Mistakes to Avoid

While ~au is a simple grammar point on the surface, there are a few “traps” that foreign learners often fall into. Let’s look at how to navigate these so you can use the grammar with confidence.

The Subject Must Be Plural

This sounds obvious, but it’s the most frequent mistake. Because ~au implies a reciprocal action, you cannot use it with a single subject. You can’t say “I tasukeau (helped each other) my mom.” It must be “My mom and I tasukeau.”

Wrong: 私は彼と話し合いました。(I discussed him – sounds like you discussed his case with someone else)
Right: 私たちは話し合いました。(We discussed it together.)

If you want to use “with” (to), you should use the particle to. For example: Kare to hanashiau (to discuss with him). This phrasing technically has a singular subject (I), but the to creates the “partner” necessary for the reciprocal action.

Not Every Verb Can Pair with ~Au

This is where things get a bit tricky. Not every action can be reciprocal. For example, you can’t really say Tabeau (to eat each other) unless you are talking about something very strange!

Verbs that work with ~au usually involve communication, perception, or physical interaction. Common ones include:

• Shinjiau (to trust each other)
• Aishiau (to love each other)
• Naguriattta (to hit each other / get in a fistfight)
• Koriau (to compete with each other)

If the action is something you do “separately but together” (like eating at the same table or running a race in the same lane), you should stick to Issho ni + Verb. Use ~au only when the action is directed at the other person.

The Difference Between ~Au and ~Issho ni

Many students ask: “Can’t I just use issho ni?” You can, but the meaning changes slightly. Issho ni focuses on the location or time (doing the same thing at the same place). ~Au focuses on the interaction.

Compare these two:
1. Issho ni utau: We are singing the same song together (maybe in a choir).
2. Utaiau: We are singing to each other (like a musical duet where you respond to one another).

In your JLPT exam, if the context of the sentence emphasizes a bond or a back-and-forth exchange, ~au is almost always the correct choice over a simple “issho ni” construction.

Advanced Usage: Beyond the Basics

As you move toward N2 and N1, you’ll find that ~au also appears in some idiomatic expressions where the “reciprocal” meaning is a bit more abstract. For example, Ma-ni-au (to be on time) actually uses the kanji for au, though it’s treated as a set phrase now.

Another common advanced use is Kumi-合わせる (kumiawaseru), which means “to combine.” While this uses the causative form of au, it stems from the same idea of things “fitting together.”

When studying for the JLPT, pay close attention to the Reading Section. You will often see ~au used in stories to describe the atmosphere between characters. If a couple is “staring at each other” (mitsume-au), it conveys a sense of intimacy that “looking” (miru) simply cannot match. Understanding these nuances will help you better grasp the emotional tone of the text.

Conclusion: Bringing People Together with Your Japanese

Learning Japanese is about more than just memorizing vocabulary; it’s about learning how to express the invisible threads that connect us to others. The suffix ~au is one of the most powerful tools in your kit for doing exactly that. It transforms a list of individual actions into a narrative of partnership, cooperation, and mutual understanding.

To recap what we’ve learned today:

• ~Au turns a verb into a reciprocal action (doing it to each other).
• Connect it by adding ~au to the Masu-stem of the verb.
• It is commonly used for communication (hanashiau), support (tasukeau), and shared emotions (waraiau).
• Remember that the action must be directed toward one another, not just done at the same time.

The next time you are talking with your Japanese friends or language partners, try to find an opportunity to use ~au. Instead of saying “Let’s help each other” using a long sentence, try “Tasukeaimashou!” It sounds much more natural and shows that you’ve truly begun to understand the heart of the language.

Good luck with your JLPT studies! Keep practicing, keep connecting, and most importantly, keep hagemashiau (encouraging each other) with your fellow learners. You’ve got this!

Summary Checklist for Your Notes

Form: [Verb Masu-stem] + 合う
Meaning: To do [verb] to/with each other.
JLPT Level: Primarily N3 (but essential for N2/N1 fluency).
Key Examples: 話し合う (Discuss), 助け合う (Help each other), 信じ合う (Trust each other), 知り合う (To get to know each other).

Happy studying!

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