後悔する

The Japanese verb 後悔する (koukai suru) is a profound and frequently used expression that translates to "to regret." While the English word "regret" can sometimes feel formal, in Japanese, koukai suru covers a vast spectrum of human emotion, ranging from the trivial—like ordering the wrong dish at a restaurant—to the life-altering, such as choosing the wrong career path or failing to tell someone how you truly feel before they depart. It is a compound verb consisting of the kanji 後 (after/behind) and 悔 (regret/repent). Literally, it describes the feeling of looking back and wishing things were different. This word is essential for B1 learners because it allows for the expression of complex personal narratives and the discussion of past mistakes, which is a key component of natural conversation. Unlike the word zannen (disappointing), which often describes external circumstances, koukai suru focuses on internal agency—the feeling that you did something (or failed to do something) that you now wish to change. In Japanese culture, the concept of reflection (hansei) is highly valued, and koukai suru serves as the emotional bridge to that reflection. It captures the heavy, lingering weight of the 'what ifs' that haunt the human mind.

Core Nuance

The internal emotional pain resulting from one's own past actions or inactions.

In daily life, you will hear this word used in various contexts. For instance, after a long night of drinking, someone might say, "Kinou wa nomi-sugite koukai shite iru" (I'm regretting drinking too much yesterday). In more serious literature or dramas, a character might lament, "Isshou koukai suru koto ni naru" (I will end up regretting this for the rest of my life). The verb is often paired with the grammar pattern ~te shimau to emphasize the unintended or unfortunate nature of the regret, as in koukai shite shimatta. It is also frequently found in the negative form, koukai shinai, as a motivational phrase: "Koukai shinai you ni ganbarou" (Let's work hard so we don't have regrets). This proactive use of the word highlights a cultural emphasis on living a life of intention to avoid the bitterness of looking back with sorrow. Understanding the weight of this word helps learners navigate social situations where expressing humility or personal growth is required.

Grammatical Category

Suru-verb (Group 3). Conjugates like any other suru-verb (koukai shimasu, koukai shita, koukai shinai).

The word also appears in many set phrases. One of the most famous is the proverb koukai saki ni tatazu, which means "regret never comes first" or "it's no use crying over spilled milk." This implies that no matter how much you regret something later, you cannot change the past. This pragmatic view of regret is common in Japanese discourse. Furthermore, koukai suru is distinct from zannen because zannen is an adjective describing a situation, whereas koukai suru is an action of the heart. If your flight is canceled due to weather, that is zannen. If you missed your flight because you overslept, you koukai suru. This distinction is vital for sounding natural. By mastering this word, you gain the ability to express the depth of your experiences and the lessons you have learned from your mistakes.

Synonym Note

Kuyamu (悔やむ) is more emotional and often used for mourning or deep, lingering sorrow, while koukai suru is more common in daily speech for general regret.

Using 後悔する (koukai suru) correctly requires an understanding of how to connect it to the action being regretted. The most common structure involves using the past tense of a verb followed by the nominalizer koto and the particle wo. For example, "I regret eating" becomes tabeta koto wo koukai suru. This structure clearly identifies the specific event that triggered the regret. Another common pattern is using the conditional form ~ba yokatta (I wish I had...) followed by to koukai suru. This adds a layer of "I should have done X" to the statement, making it more descriptive of the speaker's internal state. For instance, "I regret not buying it" can be expressed as kawanakereba yokatta to koukai shite iru. This versatility makes koukai suru a powerful tool for storytelling and personal expression.

Pattern 1: [Verb Past] + koto wo koukai suru

Focuses on the specific action. Example: 'Kanojo to wakareta koto wo koukai shite iru' (I regret breaking up with her).

In formal settings, koukai suru is often used in the potential or passive forms to discuss broader organizational or social mistakes. For example, koukai sareru (to be regretted) might appear in a business report discussing a failed project. However, in most everyday interactions, the active form is used to express personal feelings. It is also important to note that koukai is a noun, and can be used with particles like ni or no. For example, koukai no nai jinsei means "a life without regrets." This is a common theme in Japanese graduation speeches and self-help books. When using the verb, the degree of regret can be modified with adverbs like hageshiku (intensely), fukaku (deeply), or sukoshi (a little). These modifiers allow the speaker to calibrate the intensity of their emotion accurately.

Pattern 2: [Verb-ba] + yokatta to koukai suru

Expresses regret through the lens of a missed opportunity. Example: 'Motto hayaku kureba yokatta to koukai shita' (I regretted that I should have come earlier).

Furthermore, koukai suru can be used in the negative to express determination. Phrases like "koukai wa shitakunai" (I don't want to regret) or "koukai sasenai" (I won't make you regret) are common in romantic or professional commitments. In these cases, the word moves from describing a past feeling to setting a future intention. This shift is crucial for learners to recognize, as it changes the tone from lamentation to resolve. When speaking to superiors, use the polite form koukai shite orimasu to show a humble acknowledgment of a mistake. In casual conversation among friends, koukai shichatta is a softer, more natural way to admit a minor blunder. By varying the conjugation and the surrounding grammar, you can fit koukai suru into almost any social context.

Pattern 3: [Noun] + wo koukai suru

Directly regretting a choice or noun. Example: 'Sentaku wo koukai suru' (To regret a choice).

In the real world, 後悔する (koukai suru) is a staple of Japanese emotional vocabulary. You will encounter it frequently in Japanese pop culture, particularly in music and television dramas. J-Pop lyrics often revolve around themes of unrequited love or past mistakes, where phrases like "koukai bakari no hibi" (days full of nothing but regret) appear to tug at the listener's heartstrings. In anime, protagonists often scream about their regrets before finding the strength to change their fate, or villains express a final moment of koukai before their defeat. This makes the word feel very dramatic, but it is equally at home in a mundane office setting. For instance, a colleague might mention, "Kono keiyaku, koukai suru koto ni naranai ka na?" (I wonder if we'll end up regretting this contract?), reflecting a cautious, risk-averse business culture.

Media Usage

Common in song titles and lyrics (e.g., 'Koukai no Uta') and dramatic dialogue in movies.

Beyond entertainment, koukai suru is used in news reporting and documentaries. When a public figure makes a mistake, they might state in a press conference, "Fukaku koukai shite orimasu" (I am deeply regretting this), as part of a formal apology. In daily conversations, it is often used when discussing health and lifestyle choices. You'll hear Japanese people talk about koukai when they eat too much junk food, skip the gym, or stay up too late watching YouTube. It’s a word that bridges the gap between serious life philosophy and everyday human fallibility. If you're shopping with a friend and they're hesitant about a purchase, you might encourage them by saying, "Kawanai to koukai suru yo!" (You'll regret it if you don't buy it!). This usage shows that the word is not always heavy; it can be used lightheartedly to nudge someone toward a decision.

Common Context

Purchasing decisions, romantic relationships, career moves, and health habits.

In educational settings, teachers might use the word to motivate students. "Ima ganbaranaito, shiken no ato de koukai suru koto ni narimasu" (If you don't work hard now, you will end up regretting it after the exam). This highlights the role of koukai as a cautionary concept in Japanese society. It is also a key word in literature, where internal monologues often dwell on koukai to build character depth. Whether it's a high-stakes legal drama or a simple chat about lunch, koukai suru is the go-to verb for expressing that universal human feeling of wishing the past could be undone. By paying attention to how native speakers use it, you'll notice it's often followed by a resolution to do better next time, connecting the regret to the positive concept of kaizen (continuous improvement).

Nuance Check

Unlike 'regret' in English which can be a formal polite expression (e.g., 'We regret to inform you'), koukai suru is almost always about genuine emotional feeling.

One of the most frequent mistakes English speakers make with 後悔する (koukai suru) is using it to translate the formal "regret" used in business correspondence. In English, you might say, "We regret to inform you that your application was denied." In Japanese, using koukai suru here would sound incredibly strange and overly personal, as if the company is having an emotional breakdown over your application. Instead, formal Japanese uses phrases like zannen nagara (unfortunately) or moushiwake gozaimasen ga (we are terribly sorry but). Koukai suru is strictly for the emotional feeling of regret, not for formal politeness. Another common error is confusing koukai suru with zannen. Remember: zannen is an adjective for a situation you can't control, while koukai suru is a verb for something you feel you could have controlled.

Mistake 1: Formal Notification

Don't use it for 'We regret to inform you.' Use 'Zannen nagara...' or 'Ainuite...' instead.

Another mistake involves the particle usage. Some learners try to use koukai suru like ayamaru (to apologize) and use the particle ni for the person they are apologizing to. However, koukai suru is an internal feeling. You don't "regret to someone"; you regret an action. If you want to say you feel bad toward someone, you should use moushiwake nai or moushiwakenaku omou. Additionally, learners sometimes forget to use the past tense of the verb when describing the action they regret. It’s not "I regret to go," but "I regret that I went" (itta koto wo koukai suru). Using the present tense makes the sentence grammatically awkward and confusing for native speakers. Mastering the [Past Verb] + koto wo structure is the best way to avoid this.

Mistake 2: Confusing with 'Zannen'

Zannen = 'It's a pity (external).' Koukai = 'I regret (internal).'

Finally, be careful with the intensity. Since koukai suru is a strong word, using it for very minor things might sound a bit melodramatic unless you are being intentionally funny. For example, saying "I deeply regret buying this 100-yen pen" might get a laugh, but if you're serious, it sounds like you have very high stakes for stationery. In those cases, a simple "shippai shita" (I messed up) or "kawanakya yokatta" (I shouldn't have bought it) is more natural. Also, don't confuse koukai (後悔) with koukai (公開 - public/open to the public) or koukai (航海 - voyage). They are homophones but have completely different kanji and meanings. Context usually makes it clear, but in writing, the kanji is essential.

Mistake 3: Homophones

後悔 (Regret) vs. 公開 (Public) vs. 航海 (Voyage). Watch your kanji!

While 後悔する (koukai suru) is the most common way to say "regret," Japanese has several other words that capture similar feelings with different nuances. Understanding these can help you choose the right word for the right situation. The most closely related verb is kuyamu (悔やむ). While koukai suru is often used for specific decisions, kuyamu is more emotional and lingering. It is often used in the context of mourning (okuyami) or deep, soulful regret that you can't stop thinking about. If koukai is a sharp pain from a mistake, kuyamu is the long ache that follows. Another important alternative is hansei suru (反省する). While koukai is purely about the negative feeling, hansei is about reflecting on the mistake to learn from it. In Japanese schools and companies, hansei is seen as a positive, necessary step toward improvement.

Comparison: Koukai vs. Hansei

Koukai focuses on the 'bad feeling' of the past. Hansei focuses on 'learning' for the future.

For more casual situations, you might use zannen (残念) or oshimum (惜しむ). As mentioned before, zannen is for disappointment about things outside your control. Oshimum, on the other hand, means to "begrudge" or "value something too much to let it go." For example, wakare wo oshimum means to be reluctant to part ways. It’s a form of regret, but more about the loss of something good rather than the guilt of a bad action. If you want to express a lighter "I messed up" feeling, shippai shita (I failed/messed up) is often used where an English speaker might say "I regret." For example, if you overcook dinner, you'd say shippai shita! rather than koukai shite iru. Choosing between these words depends on whether you want to emphasize the guilt, the lesson, the disappointment, or the loss.

Comparison: Koukai vs. Kuyamu

Koukai is intellectual/action-based. Kuyamu is emotional/feeling-based.

Finally, in literary or very formal contexts, you might see kaikon (悔恨), which means "remorse." This is a much heavier word than koukai and is usually reserved for serious moral failings or tragic life stories. For most B1 and B2 level conversations, koukai suru is your most versatile and reliable word. It covers about 90% of the situations where you'd want to express regret. By learning these alternatives, you don't just expand your vocabulary; you gain a better understanding of the Japanese emotional landscape, which values the distinction between self-blame, self-improvement, and simple disappointment. This cultural literacy is just as important as the grammar itself.

Comparison Table

• 後悔 (Koukai): General regret for actions.
• 反省 (Hansei): Constructive reflection.
• 悔やむ (Kuyamu): Deep emotional sorrow/mourning.
• 残念 (Zannen): External disappointment.
• 失敗 (Shippai): A mistake or failure.