Desu: What It Means, and When and How to Use It - 80/20 Japanese (2024)

“Desu”「です」 is one of the first words that most Japanese language students encounter, yet it is also one of the most misunderstood.

Far too many people are mistakenly led to believe that it just makes a sentence polite, and although that is effectively all it does in some cases, it is so much more than that.

In this article, I will cover it all – from the simple, beginner-level uses of “desu” in polite sentences, to all the various forms it takes and the deeper reasoning behind why “desu” seems to be completely inconsistent with everything else in Japanese grammar.

Contents

• What “Desu”「です」 Means – The Simple Answer
• Where “Desu”「です」 Fits Into the Overall picture
• Japanese Predicates
  • Verb Predicates
  • Noun + Copula Verb Predicates
  • I-Adjective Predicates
  • Na-Adjective Predicates
• Adding ‘Other Information’
• Key Takeaways

What “Desu” Means – The Simple Answer

“Desu” is the polite form of the copula verb meaning “to be” or “is”. It is the verb used to describe two things as being equal, that is, X = Y. Typically, this will be done using the pattern:

X wa Y desuX は Y です。

It is easy to think that “wa”「は」 means “is” or “equals” here, but it doesn’t. “Wa”「は」 plays a different role, as we’ll see below.

Here’s a real example following the above pattern:

In this sentence, we have three parts:

• The topic, “kyō”「今日きょう」, marked by the particle “wa”「は」. This simply tells us we are talking about “today”.
• “Getsuyōbi”「月曜日げつようび」, meaning “Monday”
• “Desu”「です」, which tells us that the thing before it – “getsuyōbi”「月曜日げつようび」 – is “equal” to the topic, “kyō”.

We could better approximate this sentence in English as:

Speaking of today, Monday is.

What “Wa”「は」 Means (Hint: It’s not “is”)

As I mentioned, it is easy to fall into the trap of thinking that the particle “wa”「は」 is what tells us that today is equal to Monday. It’s not.

In this sentence, as always, “wa”「は」 simply tells us what we are talking about for this sentence. In this case, that is “today”, so everything we say after “wa”「は」 is in relation to today (read about the difference between “wa”「は」 an “ga”「が」 here). So, in essence:

Kyō wa今日きょうは = (About) today

For comparison, here’s another sentence starting with this that doesn’t end in “desu”:

You can see here that “wa”「は」 does not mean “is”. It simply tells us what we are going to be talking about for the rest of the sentence. Remember this well, because it is always true.

So, in our “desu”「です」 sentence, what follows “wa”「は」 is: getsuyōbi desu月曜日げつようびです

• Getsuyōbi月曜日げつようび = Monday
• Desuです = is

Combine everything and we get:

kyō wa getsuyōbi desu今日きょうは月曜日げつようびです = About today, is Monday

Or, in more natural English, Today is Monday.

Remember, our general sentence pattern again for simple X = Y sentences is:

X wa Y desuX は Y です。

An important point to understand here is, what can X and Y be?

Basically, X will always be a noun, while Y can be either a noun or an adjective. This includes simple nouns and adjectives, as well as more complex elements like complex noun phrases or negative and past-tense adjectives.

Here’s an example where Y is an adjective:

The same logic applies here as earlier.

A Deeper Understanding

What we have covered so far is enough to understand and use “desu”「です」 in simple sentences.

Unfortunately, however, if we try to take this simple approach much further, our understanding of “desu”「です」 can become a bit questionable. This is because the informal equivalent of “desu”「です」 takes different forms depending on the situation, including, in some cases, no form at all!

To truly understand “desu”「です」, we need to take a close look at what role it plays in different situations.

Understanding the role of “desu”「です」 will make it much easier to determine when we should (and shouldn’t) use it, and in what form.

Perhaps more importantly, a proper understanding of “desu”「です」 will also give us a more complete picture of Japanese grammar and sentence structure as a whole.

For the remainder of this article, I’m going to explore in depth the practical uses of “desu”「です」 and its underlying purpose in different situations. By the end, you should have a fairly clear understanding of what “desu”「です」 is, when you should use it, and, perhaps most importantly, how it fits into the overall Japanese grammar system.

Where “desu”「です」 fits into the overall picture

To really understand what “desu”「です」 is, it will help a lot if we first have a clear idea of how Japanese sentences of all types are structured. To use a bad analogy, a car is much more useful if we have proper roads to drive it on.

Let’s start by looking at the sentence structure model that we’ll be squeezing “desu”「です」 into:

If you haven’t seen this before, I highly recommend reading my article on Japanese sentence structure first before continuing.

The green “Verb” section is labelled as such because most of the time, in simple sentences where the verb is not “desu”「です」, that is all that goes there – a verb.

The truth is, however, that it would be more accurate to label the green section as the “predicate”, like so:

What’s a predicate, you ask?

It’s a scary sounding term, but it’s not too difficult to understand on a basic level, and it will help us tremendously in understanding what “desu”「です」 does, and how it compares to other verbs.

From Wikipedia*:

The predicate of a sentence mostly corresponds to the main verb and any auxiliaries that accompany the main verb.

(*There are actually competing definitions of the predicate, but this one from modern linguistic theory is what I’ll be using.)

In other words, in most cases, it’s just the main verb of the sentence, but sometimes this verb has a couple of other things attached to it.

Let’s look at a simple example in English:

Yoshi ate yakisoba.

Here, the main verb is “ate”, and the predicate is also “ate”. Now, here are a few similar sentences that have a different, more complex predicate. The predicates are in bold:

Yoshi did not eat yakisoba.

Yoshi is eating yakisoba.

Yoshi should eat yakisoba.

Yoshi will be eating yakisoba.

Notice that everything other than the predicate is exactly the same in each of these sentences, while the predicate itself varies considerably. Words like “did” and “not” are examples of the auxiliaries to the main verb that Wikipedia’s definition of the predicate is referring to.

One way to think of the predicate is to call it a “verb phrase”. This probably makes more sense intuitively, but we can’t technically call it this because “verb phrase” is actually a real term used to describe something else. Chances are you don’t care about that, though, so if it helps, any time you see the word “predicate” in this article, just think of it as meaning “verb phrase”.

Japanese predicates

In Japanese, the concept of the predicate is essentially the same, but the types of predicates that exist are different to English.

For simple sentences with a single verb, the predicate is just the main verb, the same as we saw in English:

Since the verb is the predicate, we can put this into our diagram and use either title to label the green section:

For simple sentences like this, the “Verb” label makes sense because it is obviously much easier to understand (while still being accurate).

However, Japanese has other predicate forms where the “verb” label doesn’t really make sense. Here are the four types of predicates in Japanese:

• Verbs (not including “desu”「です」, the copula verb – to be explained shortly)
• Noun + copula verb (desuです)
• I-adjectives
• Na-adjectives

We could incorporate these into our diagram like this:

This is fundamentally different from English, which as we know only has predicates made up of verbs plus any extra bits like “not” and “will”. Here’s an example:

(Again, for more about this concept, check out my sentence structure article.)

In both languages, complete sentences must contain a predicate. In Japanese, that’s actually all they need, while English sentences have a couple of additional requirements, which we won’t go into.

Note: Despite what I’ve said previously, Japanese sentences do not actually need a verb to be grammatically complete. What they need is a predicate, though much of the time the predicate will explicitly include a verb anyway. English sentences also need a predicate, but the difference is that predicates in English must include a verb.

This explains why Japanese people will say things like “oishī!”「おいしい！」 (delicious) or “kawaī!”「かわいい！」 (cute), where in English we would normally add other words in order to form a complete sentence, such as “That is so cute!”.

In Japanese, these adjectives on their own are predicates – that is, “verb phrases” that alone are enough to form a complete sentence. This is not true in English, hence the need for additional words like “that is”. Adding words like this in Japanese, however, would generally be redundant.

These additional predicate forms are also why “desu”「です」 might seem confusing and inconsistent. Apart from pure verb predicates, “desu”「です」 is necessary in all three of the other predicate types when using polite Japanese – the same three types that do not exist in English.

So, if we want to truly understand “desu”「です」, it is actually quite simple – we know that the green part of our diagram is where the predicate goes:

Now we just need to understand how “desu”「です」 fits into each of the different predicate forms. Let’s look at those now, starting with the one we are already familiar with.

Verb Predicates

We already know what to do with verbs other than “desu”「です」, but it will help to include them as a reference point for the other predicate types.

So, for the sake of comparison, here is the verb “tabemasu”「食たべます」 (to eat) in the present, past, negative, and negative past tenses, in both polite and informal Japanese:

These will be more relevant soon. If some of them are new to you, don’t worry – you don’t need to be familiar with them to understand the main concepts in this article.

Noun + Copula Verb Predicates

One of the uses of “desu”「です」 is as a “copula” verb, which is a special kind of verb seen in most (if not all) languages. Generally, copula verbs are used to express something equivalent or similar to:

A = B

Example:

Yoshi = a student

In English, we write this as:

Yoshi is a student.

In polite Japanese, we write this as:

“Is” and “desu”「です」 are the verbs that link the two other words (Yoshi and student/gakusei学生がくせい) together, defining one as equal to the other. This verb is the most common copula verb. (There are other copula verbs, and they vary between languages, but we don’t need to worry about them here.)

So, if “desu”「です」 is a copula verb, and one of the types of predicates in Japanese is “noun + copula verb”, then in this sentence (where “gakusei”「学生がくせい」 is a noun), our predicate must be…

We can therefore put this into our diagram like this:

If we compare this to our first sentence, we can see that they both fit the same structure – as long as we remember that:

• the green section should be labelled “predicate” (not “verb”); and,
• Japanese has different types of predicates that do not exist in English.

With that knowledge, we can represent any sentence that Japanese might throw at us using the same old diagram.

One thing to note here is that in the case of sentences with a “noun + copula” predicate, we can’t really use most of the elements in the “Other information” section. They just don’t make sense.

What I mean by that is that we can’t include things like objects, as we did in our previous sentence:

Doing this with “gakusei desu”「学生がくせいです」 as the predicate would result in something absurd like this:

It’s the same for most of the “Other information” elements, with a few exceptions. There are certainly lots of situations where you can use the subject (gaが), and some other elements may work in certain situations too, but most of the ones shown here generally need the predicate to be a verb that describes an action, which a “noun + desuです” predicate is not.

Taking it a step further (more advanced)

Some “Other Information” elements may seem like they can be used with a “noun + desuです” predicate based on the fact that they make sense if we just write them out in English. However, in these cases, the relationship between the words is often not the same. Here’s an example:

Yoshi is a student from Japan.

This does make sense, but we cannot translate this into Japanese as:

× yoshi wa nihon kara gakusei desu.

× よし は にほん から がくせい です。

× よしは日本にほんから学生がくせいです。

To understand why this works in English but not in Japanese, it will help to define this sentence in terms of “A = B”. Let’s see:

Yoshi = [a student from Japan]

Importantly, [a student from Japan] is a single “thing” (in this case a person), and in both English and Japanese, this single thing is expressed using a noun phrase.

The noun phrase we need here is:

a student from Japan

nihon kara no gakusei

にほん から の がくせい

日本にほんからの学生がくせい

This (or perhaps alternatively, “nihon kara kita gakusei”「日本にほんから来きた学生がくせい」) is the noun that forms the “noun” part of the [noun + desuです] predicate, hence we would include this in our diagram like so:

I won’t go into any more detail on noun phrases here, but they are incredibly powerful and allow us to build all manner of complex sentences. They’re also not as complicated as they probably seem. If you’re interested, my book has an entire chapter on them that explains all the variations of noun phrases and how to use them in sentences.

Now that we can see how “noun + copula verb” predicates fit into a sentence, let’s see how we can modify them in the same way that we modify basic verb predicates. We’ll start with…

We simply conjugate our copula verb into the past tense, just like we do with regular verbs. The diagram is essentially the same as before:

Let’s see how we would express the predicate “gakusei desu”「学生がくせいです」 in other forms:

These are all predicates, and can therefore be substituted into the green part of our sentence, just like “gakusei desu”「学生がくせいです」:

Importantly, these predicates are all of the form:

Noun + copula verb

Our noun is obviously still just “gakusei”「学生がくせい」, so the second part of these predicates are, in effect, all just different forms of the copula verb “desu”「です」.

I-Adjective Predicates

To understand these types of predicates, we need to look at i-adjectives (as well as na-adjectives) a certain way – and not the way you are probably used to.

I-adjectives and na-adjectives are often thought of as simple words, but we need to treat them as words that behave like verbs. Because, well, in many ways they do.

For i-adjectives, this is a bit more obvious, since we conjugate them when making them negative, putting them in the past tense, or both. For example:

Now, these can all be used in two different ways:

1. To modify a noun (eg. oishī yakisobaおいしい焼やきそば)
2. As a predicate

Option 2 is obviously what we are concerned about here, so let’s try putting “oishī”「おいしい」 into a sentence as the predicate:

If we compare this to the other predicate forms we’ve looked at so far, you might notice that something seems to be missing…

Where’s the verb? The first one has an obvious verb, and the second has the copula verb “desu”「です」, but what about the last sentence?

As I noted earlier, Japanese sentences do not actually need a verb to be grammatically complete – they need a predicate.

Since i-adjectives are by themselves predicates, sentences like the following are grammatically complete:

This is correct informal Japanese meaning, “Yakisoba is delicious”, even though there is no word that means “is”.

How is this possible?

Because in this case, “oishī”「おいしい」 is the predicate – a “verb phrase” that effectively includes the meaning of the verb “to be” within itself.

Hence, in this context, “oishī”「おいしい」 effectively means, “is delicious”.

That’s right – Japanese adjectives behave like verbs in some situations. They are basically super-words that are both adjectives and verbs rolled into one. This is very different to English.

Polite forms of i-adjective predicates

Hopefully you can now see how i-adjectives can be used as the predicate in a sentence, but we’re still missing something…

When we listed out the various conjugations of “tabemasu”「食たべます」 and “gakusei + desu”「学生がくせい + です」, there were two versions of each – an informal one and a polite one.

We need polite versions of i-adjective predicates too. Here they are:

Yep. We just add “desu”「です」 to each. These are the polite predicate forms of i-adjectives.

Let’s try putting one into our diagram:

So, just as we change the politeness of a regular verb sentence by changing the form of the verb…

… and we change the politeness of a [noun + copula verb] sentence by choosing a different form of “desu”「です」…

… we make a sentence with an i-adjective predicate polite or informal by choosing the appropriate form of the adjective.

Informal:

Polite:

Important! I-adjectives are not always predicates!

It’s important to note that as per option 1 of our ways to use adjectives, we can also put “oishī”「おいしい」 before a noun. Adjectives in Japanese are not always predicates!

Take this example:

Here, “oishī”「おいしい」 is not a predicate, and does not behave like a verb at all.

This is what’s called the “attributive form”, and it just means “delicious”, nothing more. It just so happens that for i-adjectives, the attributive forms and the (informal) predicate forms are the same (unlike na-adjectives, as we’ll soon see).

This is always the case. That is, adjectives that appear directly before nouns as part of a noun phrase always take their attributive form – even in other tenses, such as if we changed it to “oishikunai yakisoba”「おいしくない焼やきそば」.

Always remember, i-adjectives can be either of the following:

• adjective/verb super-word predicates (used at the end of a sentence/clause)
• adjectives in the attributive form (used before a noun)

I-Adjective Summary

For practical purposes, the main points to remember are:

1. When i-adjectives end a sentence, they are basically an adjective/verb super-word meaning “is [adjective]”.
2. The polite form of that super-word is just the adjective itself (in the appropriate form) plus “desu”「です」.
3. When an i-adjective is used before a noun, it is not the sentence predicate, so it does not have a polite form (ie. don’t add “desu”「です」).

Na-Adjective Predicates

Given what we now know about the other predicate types, na-adjective predicates should be pretty easy. Let’s see how we deal with them.

Here are the same eight predicate forms of the na-adjective “yūmei”「有名ゆうめい」, which means “famous”:

You’ll notice that these are all exactly the same as they were for “noun + copula verb” predicates like “gakusei + desu”「学生がくせい + です」:

In terms of meaning, however, they are obviously more like i-adjectives, as both i- and na-adjectives are descriptive words. They do not represent things like nouns do.

So, we can look at na-adjectives one of two ways.

The first option is to say that each of the above variations are conjugations of the na-adjective predicate “yūmei da”「有名ゆうめいだ」, just as the i-adjective variations were conjugations of the predicate “oishī”「おいしい」.

The second option is to just say that the “da”「だ」 or “desu”「です」 after a na-adjective is a separate word – the copula verb “desu”「です」, to be precise:

Predicate form = [na-adjective + copula verb]

In this case, they are the same as [noun + copula verb] predicates in almost every way.

Just beware, however, that if looked at this way, the predicate form is [na-adjective + copula verb], not just “na-adjective” as described above. A na-adjective alone (without a form of “desu”「です」) is not a predicate, and thus cannot be used to complete a sentence.

Ultimately, it doesn’t really matter how you look at it – choose the one that makes sense to you. The result will always look something like this:

Either way, it is important to remember that an appropriate variation of “desu”「です」 (eg. da, desh*ta, datta,だ, でした, だった, etc.) needs to follow “yūmei”「有名ゆうめい」 and other na-adjectives in order for them to include the “to be” meaning. Just like “yoshi wa gakusei”「よしは学生がくせい」 is an incomplete sentence, so is “yoshi wa yūmei”「よしは有名ゆうめい」. Without a variation of “desu”「です」, they are not predicates, and will result in an incomplete sentence.

(Of course, colloquially, we don’t always need complete sentences, but you’re better off knowing what’s correct and are able to recognize when the rules are being “broken”, as opposed to being left in the dark wondering why nothing seems to be consistent).

Attributive form of na-adjectives

Also, don’t forget that, like i-adjectives, the above only applies to na-adjectives when used as predicates.

If we use an adjective before a noun, like we did with “oishī yakisoba”「おいしい焼やきそば」, the adjective needs to be in the attributive form.

For na-adjectives, we put them into their attributive form by adding “na”「な」, which “connects” the adjective to the noun, like so:

You can see that the usage here is similar to that of attributive i-adjectives (eg. oishī yakisobaおいしい焼やきそば), except for the addition of “na”「な」. The other attributive forms of na-adjectives are the same as their informal predicate form counterparts:

Each of these can be placed before a noun to modify it. For example:

Adding ‘Other Information’

So far, all of the example sentence diagrams relating to the three non-verb predicate types have included an empty ‘Other Information’ section.

I mentioned earlier that most of the elements that might normally appear in this part of a sentence don’t get used with these predicate types because they simply don’t make sense, but there are exceptions. The one you are likely to see most often is the Subject (marked by gaが).

Let’s look at an example:

I won’t go into this too much, but this basically means, “When talking about Fujinomiya, the yakisoba is delicious.”

The topic is “fujinomiya”「富士宮ふじのみや」(a city in Shizuoka prefecture), so that is what the sentence is talking about, and the subject is “yakisoba”「焼やきそば」, which means that yakisoba is the thing that is “being delicious”, as our predicate “oishī desu”「おいしいです」 tells us.

Now, in our earlier sentence, where we just said “yakisoba is delicious”, the word “yakisoba”「焼やきそば」 was the topic, not the subject, even though it was still the thing that was “being delicious” in that case too:

The reason for this is that here, “yakisoba”「焼やきそば」 has effectively been “upgraded” from the subject to the topic. You can read more about this in my in-depth article about the difference between “wa”「は」 and “ga”「が」.

In any case, the point is that some ‘Other Information’ can be included, but only in a fairly limited number of situations.

Key Takeaways

This seemingly simple word has a lot of subtleties to it, and digging into those subtleties like we have here may leave you feeling a bit overwhelmed, but putting these lessons into practice should be much easier than the theory behind it. Let’s break down what we’ve covered.

Japanese sentences end with predicates, of which there are four types:

• Verb
• Noun + copula verb (desuです)
• i-adjective
• na-adjective

The polite forms of the last three all include “desu”「です」, which effectively means “is” or “to be”.

For [noun + copula verb] predicates, “desu”「です」 is the copula verb, so its meaning of “is” essentially tells us that [the topic (or subject) of the sentence] = [the word or phrase before“desu”「です」]. To change the tense or politeness, we just use a different form of “desu”「です」.

For i-adjective predicates, “desu”「です」 should be considered as the ending of the adjective’s polite present tense form. This is because in informal Japanese, the i-adjective can be used alone as a predicate meaning “is [adjective]”, so the base adjective effectively includes the meaning of “is” within itself. Adding “desu”「です」 puts the i-adjective predicate into its polite form, whatever tense it may be in.

Na-adjective predicates can be viewed like either of the above two predicate types, since their meaning and use is similar to i-adjectives, but their form is the same as [noun + copula verb] predicates. Either way, “desu”「です」 is used in the polite present tense of na-adjective predicates, and we change tenses and politeness by conjugating “desu”「です」.

That’s about it!

Things got pretty intense here, but I hope that this deeper understanding of what “desu”「です」 really is gives you a much clearer idea of when to use it, when not to use it, and how to use it correctly in its various forms.