かう

The Japanese verb かう (kau), typically written with the kanji 買う, is one of the most fundamental building blocks of the Japanese language. At its core, it represents the act of purchasing or buying something in exchange for money. Whether you are at a bustling convenience store (konbini) in Tokyo, a high-end department store in Ginza, or simply browsing an online marketplace like Mercari, this is the word you will use to describe the transaction of acquiring goods. For English speakers, the transition is quite direct as it maps almost perfectly to the English verb 'to buy'. However, the cultural weight of 'buying' in Japan often involves a high level of politeness and specific social scripts that a learner must master to sound natural.

Core Meaning

To acquire ownership of an item or service by paying a specific price. It is a transitive verb, meaning it always takes a direct object—the thing being bought—marked by the particle 'o' (を).

Beyond the simple exchange of cash for bread, kau is used in various metaphorical and abstract contexts. You can 'buy' into an idea, 'buy' time, or even 'buy' trouble (though Japanese has specific idioms for these). In the modern era, the word has expanded to include digital transactions. When you click 'purchase' on a smartphone app, you are still performing the action of かう. It is important to note that in Japanese, the verb does not change based on the method of payment; whether you use cash, a credit card, or a QR code payment like PayPay, the action remains kau.

In daily life, you will hear this word in various forms. The polite form, かいます (kaimasu), is the standard for interacting with shop staff or acquaintances. The casual form, かう (kau), is reserved for friends and family. Interestingly, the word is also used in the phrase kaimono (shopping), which literally means 'buying things'. Understanding the nuances of when to use the plain form versus the polite form is crucial for navigating Japanese social hierarchies. For instance, if you are discussing your weekend plans with a coworker, you would say 'Hon o kaimashita' (I bought a book), but with a close friend, 'Hon katta' would be the natural choice.

Homophone Alert

Be careful! There is another common verb pronounced kau (飼う), which means 'to keep or raise a pet'. While they sound identical, the kanji and context are completely different. You 'buy' (買う) a dog at a pet shop, but you 'keep' (飼う) a dog at home.

Furthermore, kau is used in more complex grammatical structures. For example, katte oku means to buy something in advance for future use, and katte ageru means to buy something for someone else as a favor. These variations show how the simple act of purchasing is integrated into the broader Japanese system of social obligations and preparedness. When you master kau, you aren't just learning a verb; you are learning how to participate in the Japanese economy and social fabric. From the morning coffee run to purchasing a family home, kau is the engine of daily activity.

Usage in Media

In anime and drama, you will often hear characters say 'Katte kita yo!' (I'm back and I bought [something]!). This highlights the result-oriented nature of the verb in domestic life.

Using かう (kau) correctly requires an understanding of Japanese verb conjugation and particle usage. As a 'Godan' or 'u-verb', its stem changes depending on the suffix. The most common structure you will encounter is [Noun] + を (o) + かう (kau). The particle 'o' marks the object being purchased. For example, 'ringo o kau' means 'to buy an apple'. If you want to specify where you are buying it, you use the particle 'de' for the location: 'Suupaa de ringo o kau' (Buy an apple at the supermarket).

Polite Conjugation (Masu-form)

To make the verb polite, change the final 'u' to 'i' and add 'masu'. Thus, kau becomes かいます (kaimasu). This is the version you will use most often when speaking to strangers, teachers, or in a business setting. For the past tense, use かいました (kaimashita).

One of the trickiest parts for beginners is the 'Te-form' and the past casual form. Because kau ends in 'u', it follows the rule where 'u', 'tsu', and 'ru' endings change to a small 'tsu' (っ) followed by 'te' or 'ta'. Therefore, the Te-form is かって (katte) and the past casual is かった (katta). This 'double-t' sound is essential for correct pronunciation. Saying 'kate' instead of 'katte' can change the meaning or make the word unrecognizable.

In more advanced contexts, kau can be combined with auxiliary verbs to add nuance. Katte morau means someone bought something for you. Katte ageru means you bought something for someone else. Katte kuru means to go out, buy something, and come back. This last one is extremely common in daily conversation. If you are leaving the house to get milk, you would say 'Miruku o katte kuru ne!' (I'll go buy some milk and come back!).

Negative Forms

To say you 'don't buy' or 'won't buy', use かわない (kawanai) in casual speech or かいません (kaimasen) in polite speech. Note the 'w' that appears in the casual negative form—this is a unique feature of verbs ending in 'u'.

When asking a question, you simply add the particle 'ka' at the end of the polite form: 'Nani o kaimasu ka?' (What will you buy?). In casual speech, you use a rising intonation: 'Nani kau?' (What are you buying?). The versatility of kau makes it an essential tool for any learner. It covers everything from the necessity of groceries to the luxury of a new gadget. By practicing these different forms—kaimasu, katta, kawanai, kaitai—you will be able to express a wide range of intentions and actions related to the world of commerce.

Potential Form

To say you 'can buy' something, use かえる (kaeru). This is often used when discussing whether something is affordable or available. 'Koko de chiketto ga kaeru' (You can buy tickets here).

In Japan, the word かう (kau) is omnipresent. You will hear it in the rhythmic calls of street vendors, the polite inquiries of shop assistants, and the casual chatter of teenagers at a mall. One of the most common places to hear a variation of this word is at the cash register. While staff will use more honorific language like o-kai-motome (the humble/honorific way to say buying), you as the customer will use kaimasu. For example, when pointing at an item in a display case, you might say 'Kore o kaimasu' (I'll buy this one).

At the Supermarket

You'll hear parents talking to children: 'Kore kaitai?' (Do you want to buy this?) or 'Kyou wa nani o kaou ka?' (What shall we buy today?). The volitional form kaou is very common when making collective decisions.

Television commercials (CMs) are another major source. Advertisements frequently use the imperative or suggestive forms to encourage consumers. Phrases like 'Ima sugu kaou!' (Let's buy it right now!) or 'Katte kudasai!' (Please buy it!) are standard marketing tropes. In news broadcasts, you might hear the more formal kounyuu suru (to purchase), but in interviews with 'the person on the street', people will invariably use kau to describe their spending habits or their reaction to price hikes.

Social media and the internet have also birthed new ways to hear and see this word. On YouTube, 'unboxing' videos or 'haul' videos are often titled with 'Katta mono shoukai' (Introducing things I bought). On Twitter or Instagram, people post photos of their new acquisitions with the hashtag #katta (bought). There is even a slang term pochiru, which refers to the sound of clicking a mouse button to buy something online, but the underlying concept is still kau.

In the Workplace

When discussing procurement or office supplies, colleagues might ask, 'Doko de kono pen o kaimashita ka?' (Where did you buy this pen?). Even in a professional setting, kau remains the standard verb for everyday items.

Finally, you will hear kau in the context of travel. Japan has a strong culture of omiyage (souvenirs). When people travel, they are expected to kau gifts for their coworkers and family. You will hear travelers constantly debating, 'Nani o kaou ka?' (What should I buy?) as they browse station shops. This cultural practice ensures that kau is not just a selfish act of acquisition but a social act of maintaining relationships. Whether it is a 100-yen snack or a 100,000-yen watch, the word kau is the verbal gateway to the Japanese world of things.

Public Announcements

At train stations, you might hear: 'Kippu o o-kai-motome no o-kyaku-sama wa...' (Customers who are buying tickets...). This uses the honorific form of kau to show respect to the customer.

While かう (kau) seems straightforward, English speakers often stumble on a few specific areas. The most frequent error is the confusion between kau (to buy) and its homophone kau (to keep a pet). While they sound the same, they are written with different kanji (買う vs 飼う). Using the wrong kanji in a text message can lead to hilarious or confusing results. For example, saying 'Inu o kaimashita' with the 'buy' kanji means you purchased a dog, whereas using the 'keep' kanji means you have started living with/raising a dog. In many contexts, both could be true, but the distinction is important for clarity.

The 'Te-form' Trap

Many learners forget the small 'tsu' (っ) in the Te-form. They might say kaite instead of katte. This is a major mistake because kaite is the Te-form of kaku (to write). If you tell a shopkeeper 'Kore o kaite kudasai', you are asking them to 'Please write this' instead of 'Please buy this' (or more likely, you're trying to say 'I'll buy this'). Always remember: かう → かって (katte).

Another common mistake involves the particle 'ni'. In English, we say 'I bought it from him'. Learners often try to translate this literally using 'kara' or 'ni'. While 'kara' works, 'ni' is also used to indicate the person you bought from. However, the most common mistake is using 'ni' for the location. You must use 'de' for the place where the action of buying happens. 'Suupaa ni kaimasu' is incorrect; it must be 'Suupaa de kaimasu'.

The negative casual form kawanai is also a stumbling block. Because the verb ends in 'u', many learners expect the negative to be kaanai or kanai. However, all 'u' ending verbs change to 'wa' before the 'nai' suffix. This 'w' sound is a vestige of ancient Japanese and is essential for correct grammar. If you say 'kaanai', Japanese speakers will likely understand you, but it will sound very 'foreign' and grammatically broken.

Transitivity Confusion

Sometimes learners confuse kau (to buy) with uru (to sell). While they are opposites, in the heat of a conversation, it's easy to mix them up. Remember: Kau = Keep (you get the item), Uru = Unload (you give the item).

Lastly, be careful with the potential form kaeru. It sounds exactly like kaeru (to return home) and kaeru (to change). Context usually clarifies which one is being used, but if you say 'Kaeru!' excitedly, people might think you are leaving the party rather than saying you can afford to buy something. To avoid this, always include the object: 'Kore ga kaeru!' (I can buy this!). This clarifies that you are using the potential form of kau.

Overusing 'Kau'

In very formal situations, using kau can sound a bit too blunt. When talking to a high-ranking boss or a customer, use kounyuu itashimasu or o-kai-motome ni naru. Using basic kau in these contexts is a 'mistake' of register rather than grammar.

While かう (kau) is the most common way to say 'buy', Japanese offers several alternatives depending on the level of formality, the type of item, and the context of the transaction. Understanding these synonyms will help you move from a basic A1 level to a more nuanced B1 or B2 level of fluency. The most direct formal alternative is 購入する (kounyuu suru). This is a Sino-Japanese (Kango) word, which typically sounds more academic, professional, or official. You will see kounyuu on receipts, in business contracts, and on Amazon Japan's 'Buy Now' buttons.

Comparison: Kau vs. Kounyuu

• Kau: Everyday items, casual talk, personal use. (e.g., buying milk)
• Kounyuu: Expensive items, business procurement, formal writing. (e.g., buying a fleet of cars for a company)

Another interesting alternative is 手に入れる (te ni ireru), which literally means 'to put into one's hand'. While it can mean 'to buy', it more broadly means 'to obtain' or 'to get hold of'. This is often used for rare items, hard-to-find tickets, or things you've wanted for a long time. If you finally managed to get a PlayStation 5 during a shortage, you might say 'Yatto te ni ireta!' (I finally got it!) rather than just 'katta'.

For shopping as an activity, we use 買い物する (kaimono suru). While kau focuses on the specific act of purchasing a single item, kaimono suru describes the whole process of going to the store, looking around, and buying things. If you are going to the mall for the afternoon, you say 'Kaimono ni iku' (I'm going shopping). If you are specifically buying a gift, you might use 買い求める (kai-motomeru), a more literary and elegant way to say 'to seek out and buy'.

Formal/Honorific Variants

• お買い求めになる (o-kai-motome ni naru): Honorific (Keigo) used by staff to customers.
• 買い上げる (kai-ageru): Often used by stores to mean 'to purchase from a customer' or 'to buy up'.

In slang or very casual speech, especially among young people online, you might encounter ポチる (pochiru). This comes from the onomatopoeia 'pochi', the sound of a small button being pressed. It specifically refers to impulse buying something online with a single click. Another casual term is ゲットする (getto suru), from the English 'get'. This is very common in gaming (e.g., 'Pokemon getto daze!') or when someone finds a great deal at a thrift store.

Specific Contexts

• 仕入れる (shiireru): To buy in bulk for business (stocking up).
• 購読する (koudoku suru): To buy a subscription (magazines, newspapers).
• 落札する (rakusatsu suru): To buy at an auction (winning the bid).