Japanese Sentence Structure: だ Explained

The topics of だ and its variant です are a frequent pet-peeve of mine, as they seem to often be overly simplified or poorly explained for English speaking audiences not familiar with Japanese structure and syntax. As a consequence, textbooks usually lie or omit a lot of important details that are key to making Japanese sentences easy to build and understand. This article is my attempt at clarifying things, while keeping them simple enough that even absolute beginners should be able to follow intuitively.

I go into more advanced details and exceptions later for those readers who are more advanced, but it is in no way required if you’re just starting out.

Beginner Explanation

Sentence building blocks

Japanese sentence structure is surprisingly easy to deconstruct. I won’t go into many details about the middle of sentences, because I want to focus on the sentence endings, but I will provide a quick approximate explanation of what elements can be present in a sentence (or, to be precise, a clause).

There’s four types of words in Japanese grammar:

• Verb-like words
• Noun-like words
• Particles
• Auxiliary/special words

At the moment, we can ignore auxiliary words. They just create additional complexity that we don’t need to think about.

The following key rules are all you need to remember:

1. Nouns can only be followed by a particle
2. Verbs can be followed by nouns, other verbs, or certain particles
3. Particles can be followed by verbs and nouns
4. Only verbs can end a sentence

Following rule 1 and 3:

• Between nouns and other nouns, or a noun and its following verb, there must be a particle.

This is very simple, isn’t it? It’s quite well structured. Just one more thing…

Fundamental rule of だ

There’s just one extra fundamental rule to remember:

• If a sentence does not end with a verb (or verb-like word) we must add だ at the end.

This is the rule that every beginner must take home after reading this. If there’s one thing that you must not forget or ignore from this page, it’s this.

For more advanced or impatient learners: yes, I know what you are thinking. There are additional rules and exceptions, but if you can remember just one thing, this is it. The rest will follow naturally as you progress in your language studies (or keep reading).

What about adjectives and adverbs?

One small elephant in the room that I glossed over are the word groups for adjectives and adverbs. I plan to write a more detailed writeup on adjectives, but as a quick summary it’s really simple.

Japanese has two types of adjectives: い-Adjectives and な-Adjectives.

• い-Adjectives can be considered verbs or verb-like words;
• な-Adjectives can be considered nouns or noun-like words.

NOTE: From now on, unless specified otherwise, when I write “verb” I also mean い-adjectives. Likewise when I write “noun” I also mean な-adjectives.

As per the fundamental rule of だ, we only add だ if we are ending a sentence with a な-adjective (だ takes the place of な in this case). For い-Adjectives we just leave the だ out.

Adverbs attach to verbs, so they are not a concern of ours for the purpose of ending sentences and you can safely ignore them for now.

Example Sentences

• 昨日、ご飯を食べた
• 車は速い
• トムはとても元気だ
• 日本語ができる人だ
• かわいい女の子だ
• よかったら、彼にれんらくしてください

Intermediate Explanation

From this section onwards, I assume that the reader has a more adequate mastery of the fundamentals of the Japanese language. Examples and explanations will refer to grammatical rules that, if unclear, should be looked up by the reader as an exercise of independence (Unlocking Japanese: Tricks).

What about です？

です can be seen as a special case that supersedes だ in certain sentences and structures. All things considered, it’s not a bad idea to regard です as a polite variant of だ, however it is important to remember that です cannot always replace だ. The opposite is also true, there are some applications of です that cannot be replaced by だ either. I write more on this in a later section.

To keep it straightforward, the general simplistic explanation is that です adds a level of politeness on top of だ, just like the ます helper verb/conjugation adds a level of politeness to verbs at the end of a sentence. If you are speaking or writing in a register that uses ます, and the sentence does not end with a verb in ます form, you add です at the end.

Embedded Clauses

One of my favorite components of the Japanese language is embedded clauses. An embedded clause is basically a sentence that is contained within another sentence, usually by means of indirect quoting (と particle) or similar grammatical constructs.

When embedding clauses inside a larger sentence, the embedded clause must follow the fundamental rule of だ. This means that だ will not only be at the end of the sentence, but at the end of the embedded clause too.

As always, words that can end a sentence on their own must not have だ added as they become embedded. They can naturally connect to the following construct (usually the と particle) independently.

Examples:

• 部屋に入ると、臭いと言いました
• 買いに行かなきゃと思ってた
• 元気な男だと言った

Special particles that attach after だ

There are some particles that can be placed after だ (and sometimes です) when it is in a sentence-ending position. This is the first real exception to the fundamental rule of だ. For all intents and purposes, the sentence construction does not really change, it’s just an extra piece of information that is attached at the end to change tone or add additional nuance/character to a sentence.

These particles are:

• よ (～だよ)
• ね (～だね)
• な/なあ (～だな/～だなあ)
• ぞ / ぜ (～だぞ/～だぜ)
• わ (～だわ)
• っけ (～だっけ)
• (だ)い (～だい)

It is important to remember that these are sentence ending particles, not clause ending particles. They cannot go inside embedded clauses.

There are two more special sentence-ending particles that should be discussed in more details: か (and its variant かい/かな) and さ. I will talk more about these later. Just keep in the back of your mind that these particles take the place of だ and are for all intents and purposes an actual exception to the rule.

Adversative conjunctions

There is a special group of particles which are used to connect two clauses together in a larger sentence. Most of them being adversative conjunctions (e.g. “although”, “but”, etc).

These particles are placed after the clause ends, hence they also are placed in front of the だ:

• から (～だから、～)
• けど (～だけど、～) / けれど(も)
• が (～だが、～), not to be confused with the が subject particle

However, there are a lot of other particles and syntactic constructs like these that do not take だ. This is because most of them are either verb conjugations, or etymologically come from verbs, so they can work as sentence enders and do not violate the fundamental rule of だ.

The transformative particle の

の is an exceptionally annoying particle to fit around this だ rule. の is used at the end of sentences (either questions or statements) to add a nuance of interrogative or explanatory sense. It is often called the explanatory particle or form.

There are a few rules around the syntactical usage of の and I could write a whole article about it, but the gist of it is as follows.

In non-interrogative sentences:

• After verbs, の attaches cleanly and ends the sentence with だ
  • 食べる -> たべるのだ
  • 優しい -> 優しいのだ
• After nouns, the だ particle turns into な and のだ attaches to it:
  • 車だ -> 車なのだ
  • 元気だ -> 元気なのだ

In modern/colloquial usage, のだ gets contracted to んだ. The meaning and usage is exactly the same and the sentence construction does not change.

In interrogative sentences:

• After verbs, の attaches cleanly without だ
  • 食べる？ -> 食べるの？
  • 優しい？ -> 優しいの？
• After nouns, the (だ) particle turns into な and の attaches to it:
  • 車(だ)？ -> 車なの？
  • 元気(だ)？-> 元気なの？

There needs to be a special mention of what だ in parenthesis means in these interrogative sentences, however it will be explained in a later section. For the time being imagine it’s a phantom だ that can be omitted.

Relationship between だ and です

As explained earlier, です is a politeness sentence-ending particle that takes the place of だ, however it cannot always be substituted to だ (and vice-versa).

Situations where です works but だ cannot

The main purpose of です is to add politeness. It simply just happens that “だです” does not work, so です takes place of だ. It follows, however, that if you want to add politeness to a construct that does not take だ, you can still add です.

After い adjectives, which act as verbs in plain form, you cannot add だ, but you can add です as sentence ender to make the sentence polite:

• かわいい -> かわいいです

Situations where だ works but です cannot

There are some grammatical situations where politeness does not happen, so the usage of です is incorrect. In embedded (indirect) clauses, politeness is dropped, hence where there was a です, a だ is sometimes added according to the fundamental rule of だ:

• かわいいです -> かわいいと言った
• 車です -> 車だと言った
• 食べないです -> 食べないと言った

There are also some special particles mentioned earlier, that cannot work in conjunction with です because they have a conflicting politeness register:

• ～だぜ
• ～だぞ
• ～だっけ

And the special (だ)い sentence ender also cannot be used with です as the い part is attached to だ (there is no such thing as ですい).

た-form (past tense)

The た-form (colloquially referred to as the past tense) of だ is だった. Of です it is でした.

In case of a sentence in た form, we do not add だ after it as た can already end sentences on its own. Think of it like a variant/corollary to the fundamental rule of だ.

This also applies to た-form of verbs (かった for い-adjectives).

A special note about politeness: when turning です into でした, it becomes acceptable to use the particles mentioned in the previous section:

• ～だったぜ -> ～でしたぜ
• ～だったぞ -> ～でしたぞ
• ～だったっけ -> ～でしたっけ

Once again, a special mention must go to the particle (だ)い. Grammatically speaking, it is possible and accepted to use (だった)い (turn だ to だった + い), however it is not really used these days.

Instead, it is more common to use だった↗ (with rising intonation):

• 新しい仕事はどうだい？ -> 新しい仕事は(どうだったい？/ どうだった↗?)

Advanced: Details & Extras

The following sections are going to explain most of the exceptions that I have glossed over or ignored in the previous sections. Even when considering such fundamental rules of grammar like sentence construction and word order, languages are an ever-evolving entity and often natives end up breaking the rules that we usually try to stick to.

In the following paragraphs I am going to write about such colloquial exceptions or historical language evolutions that have created irregularities in the core sentence structure, sometimes even invalidating the fundamental rule of だ.

Just because they are advanced, it does not mean that they are rare. Most of these exceptions are everyday Japanese that you cannot avoid coming across, sometimes even as a beginner, so take them to heart as much as the rest of the article.

Gendered (lack-of) だ

The topic of “gender-ness” of Japanese speech could do for a whole other article, so I won’t digress too much into it. Just be aware that some words and ways of structuring a sentence can be considered more “masculine” or more “feminine”, but it’s all a big spectrum.

だ is a very “strong” way to end a sentence, and in feminine speech it can often be omitted/dropped, especially in the presence of some other softer ending particles:

• ～だよ -> ～よ
• ～だね -> ～ね
• ～だわ -> ～わ
• ～のだ -> ～の

A special mention regarding the の particle: in interrogative の sentences だ is dropped for both masculine and feminine speech. の as a feminine sentence ender is only for non-interrogative sentences.

Casual/conversational (lack-of) だ

This is probably the biggest exception and counterpoint to the fundamental rule of だ.

Similarly to the gendered paragraph above, in very casual speech (usually among friends), だ is often dropped from statements to make them sound softer and less direct/aggressive.

This means it is absolutely common to see “ungrammatical” sentences without だ like these:

• A: 元気？
• B: ん、元気！

There is one exception to this exception: even among friends, for statements that pertain to the existence of something, often with an element of surprise or exclamation, だ is often kept as a strengthening element:

• It starts to rain
• A: あっ！雨だ！
• B: 本当だな！

Sentence inversion grammar

Sometimes, as a literary device, some sentence inversion may happen. In such situations, it is common to not add だ at the end even if there should be one.

A special note needs to be made for a specific usage of the particle から. The grammar structure of XからY sometimes can be inverted in the shape of YのはXからだ. Sometimes Yのは is omitted entirely and the sentence will just be Xからだ. This goes against the usual usage of から which goes after the だ. In this usage, です is also acceptable.

Literary liberties

As is typical, when writing prose, the register usually varies a lot between authors, and the language has historically evolved in different directions from common (non-literary) usage.

It is not uncommon to find several sentences that will completely omit the だ particle even when it would not normally be.

This is common in text that makes extensive use of inverted structures and literary ”あり” style. My guess is that it’s because chaining multiple sentences with だ endings in a long text can have a very stark and declarative feeling that the author may want to avoid.

さ particle

The さ particle is a very peculiar sentence ending particle. There’s not much that needs to be said here, other than it basically takes the place of だ whenever it is used in a sentence that would be terminated with だ:

• 人生とはこんなものだ -> 人生とはこんなものさ

か / かな / かい particles

The more attentive readers should be left wondering, what happens to the か particle? It is after all one of the most used and common beginner particles to know if you want to be able to ask questions.

The truth is… か is really an annoying particle to place in this grammar writeup.

When there is politeness, it is very simple. You just add か after です (or ます) and that’s it.

However, in plain form, there are all kinds of exceptions we have to consider between だ and か. There are three general ways to ask a neutral question in a casual manner:

• これは本か？
• これは本だ↗？
• これは本↗？

Note: the arrow denotes rising intonation.

The presence of だ here makes it very hard and stark-sounding, hence it is often dropped.

However, the presence of か also makes these kinds of questions hard, and it is also often dropped.

While neither of these three variations is grammatically incorrect, the arguably most common way to ask questions in casual form is to drop both か and だ and just keep the rising intonation.

There is one combination that needs to be addressed: だか.

This can only be used inside embedded clauses (very common in forms like ～(だ)かどうか). There is a reason why a sentence like 「これは本だか？」is incorrect, and it has to do with the origin of the particle だ, however the simple explanation is that native speakers upon hearing “だか” will think of something else coming after it (similar to an embedded clause) and it breaks the flow of the conversation, so it is simply not used.

Related to the か particle is the かな self-interrogative particle. Etymologically, it’s basically just か with the な particle added at the end. It follows all the rules that か does as mentioned above, with just one slight exception. かな is a gender-neutral particle, however “な” is a mostly masculine variant of “ね”, this means the following variations can have different nuances:

• これは本か？ (neutral) -> これは本かな？(neutral)
• これは本だ↗？ (neutral) -> これは本だな? (masculine)
• これは本↗？ (neutral) -> これは本な? (…)

The last combination is a bit of a red herring. な particle alone without だ is not really used, as masculine speech tends to keep だ (see previous section on gendered speech).

Another particle related to か is かい. It can be seen as the equivalent of (だ)い except for sentences that use か instead. Their grammatical usage is almost the same, but with か instead of だ.

かしら particle

The かしら particle is another strictly feminine particle used as sentence ender. Nowadays it is mostly used only in fictional speech and has been phased out of everyday standard Japanese. However, it is still good to be able to recognize it.

Historically, かしら comes from the か + しらない verbal structure. Due to this reason, it can kind of be considered like a verb, so it can be added at the end of a sentence without requiring any だ particles to follow.

Direct vs Indirect quotes

Throughout this whole article I have talked about embedded clauses and indirect quotes, however there is a special class of embedded clauses which are direct quotes.

Such quotes are reported and embedded in a larger sentence exactly as they appear in the original sentence (hence, direct). This means they carry all kinds of politeness and particle markers that would otherwise be considered ungrammatical. They are often surrounded by 「 」(the equivalent of direct quotes in Japanese) to mark them explicitly:

• Original sentence: 日本人です
• Indirect quote: 日本人だと言った
• Direct quote: 「日本人です」と言った

Historical notes on だ

Now that you’ve made it this far, you will be rewarded with some actual nuggets of history. For the language nerds like me these kinds of discoveries are always extremely fun and enlightening, I just hope I’ll be able to amuse you as much as I have amused myself learning this.

We’ve been talking about how sentences in Japanese must end with a verb or the だ particle, but why is this the case? Why is the だ particle such an exception and how did it come to being?

Well, the explanation is actually quite fascinating. だ is a very contracted version of である.

である is a copula that simply means “to be”, but throughout the years the Japanese language has only kept this structure mostly in very formal speech and writing. As the language evolved, である kept getting slurred and contracted until it simply turned into だ:

• de aru -> de ar -> dea -> da

Similarly, its past form also received the same treatment:

• de atta -> datta

For more details on this evolution and more intricacies on the だ / である / Ø particle, I recommend: ”Da and the Zero Form as the Two Contracted Forms of the Japanese Copula” - Miyama (2010)

In modern Japanese, however, the usage of だ has slightly diverged from its original である form:

• だ cannot be used as prenominal form, while である can:
  • NであるN is valid
  • NだN is not valid (you need to use な/の, but the reason is left as an exercise for the reader)
• だ cannot appear before an expression of uncertainty like らしい or かもしれない:
  • Nであるらしい / Nであるかもしれない is valid
  • Nだらしい / Nだかもしれない is not valid (this is where the Ø particle comes into play, again an exercise left for the reader)