Da, Dearu, Desu, Masu: Choosing a Japanese Written Style

What buntai is and why it is decided first

Buntai means the style of your sentence endings, and Japanese treats it as a property of the whole document rather than of individual sentences. Before writing a single line, a Japanese writer settles one question: is this text addressed to a reader, or is it stating something into the world? An email, a letter, an announcement and most blog writing address a reader, so they take the desu-masu style. An essay, a report, a thesis, a news article and a dictionary entry state things, so they take the plain style built on da or dearu.

This is not the same decision as the spoken politeness question, though it uses the same forms. In speech you choose desu-masu or plain according to who is in front of you, and getting it wrong sounds rude. In writing there is nobody in front of you, so plain style carries no rudeness. A thesis written entirely in dearu style is not being blunt with its examiner; it is simply not addressing anyone. The other guide on polite versus casual Japanese covers the spoken half of this.

The same sentence in three styles

Two things stand out. Verbs and i-adjectives look identical in da style and dearu style, because both simply use the plain form; the styles only diverge where a noun or na-adjective needs a copula. And da style tolerates the contracted ja nai, while dearu style always writes de wa nai in full. That single contraction is a reliable giveaway of an unedited text.

Nouns, na-adjectives and the copula

The copula is where the three styles actually differ, so learn this column and the rest follows. Desu becomes da or de aru; deshita becomes datta or de atta; deshō becomes darō or de arō. Na-adjectives behave exactly like nouns here, which is why shizuka desu becomes shizuka da and shizuka de aru. In dearu style, many writers also use de aru only where the sentence needs a copula and otherwise leave verbs and adjectives bare, so a dearu-style page is not full of de aru endings.

Verbs and negatives across the styles

Verbs are the easy part: strip the masu ending and use the dictionary form, and both plain styles are satisfied at once. The negatives are where beginners slip, because the polite negative has two shapes and the plain one has spoken contractions that written style will not accept. Arimasen becomes nai; te imasen becomes te inai; and the spoken shortening te ru must be restored to te iru before it goes anywhere near a report.

One more written-register habit worth knowing: formal reports and business documents often replace te iru with te ori, as in kentō shite ori, and te kara with go. These belong to the humble written register rather than to plain style itself, so treat them as an extra layer you add on top of a desu-masu document, not as a rule of dearu style.

Connectives that belong to written Japanese

Spoken connectives sound out of place in written style, and swapping them is one of the fastest upgrades you can make to a draft. Demo, dakara, datte and ja are conversational; shikashi, shitagatte, sono tame and de wa are their written counterparts. The written set is also more precise: mata adds a parallel point, sara ni escalates, tsumari restates, tadashi adds a condition, and ippō introduces a contrasting side.

Vocabulary shifts with the connectives. Totemo becomes hijō ni, sugoku becomes kiwamete, takusan becomes ōku no, chotto becomes yaya, and iroiro na becomes samazama na. You are not making the text harder; you are removing the traces of a speaking voice.

What written style removes

• Sentence-final particles: ne, yo, na, wa, kana and zo all disappear from formal writing.
• Contractions: ja nai becomes de wa nai, te ru becomes te iru, nakya becomes nakereba naranai.
• The explanatory n da: n desu and n da become no de aru, or are simply cut.
• Hedging fillers: nanka, chotto, yappari and maa carry no information on a page.
• Direct address: anata is usually dropped, since a report does not speak to a person.
• Question marks after plain questions: written Japanese commonly ends with ka and a full stop.

Removing final particles is the hardest habit for learners who built their Japanese through conversation, because ne and yo feel like politeness. In writing they read as chatter. The written equivalent of that softening is a hedged predicate instead: to kangaerareru for it can be considered, no de wa nai ka for is it not the case that, and to iwareru for it is said that.

Converting a spoken paragraph line by line

Here is the method in one worked example. Take a spoken sentence, then apply four passes in order: fix the ending, remove the particles and contractions, replace the connective, and lift the vocabulary. Doing them in that order stops you from rewriting the meaning by accident. Each pair below shows the same content spoken and then written in dearu style.

Notice what the written version gained and lost. It gained precision, nominalised vocabulary such as gakushū and hatsuwa nōryoku, and connectives that mark logical relationships. It lost warmth, the speaker's presence and every trace of the listener. That trade is the whole point of buntai, and it is why a well-written report often sounds cold when read aloud.

Where each style actually belongs

Conventions differ by company, university and publisher, so when a template or a supervisor's example exists, copy its style rather than reasoning from first principles. The rule that never varies is internal consistency: whichever style the document opens with, it closes with.

Catching a style mix before anyone else does

Style drift almost always happens in the same three places. The first is the opening and closing lines, where polite formulas leak into a plain-style text. The second is a sentence you found difficult, where you fell back on the form you know best. The third is a bulleted list, where writers often switch to noun endings without deciding whether the whole list does so.

• Read only the last two characters of every sentence, top to bottom, ignoring the content.
• In a desu-masu document, every final should read masu, desu, mashita, masen or deshō.
• In a plain document, every final should read a verb, an i-adjective, da, de aru or datta.
• Check bullet lists separately and make them all noun endings or all sentences, not both.
• Search your draft for ja nai, te ru, n desu and ne to catch spoken leftovers in one pass.
• Read the first and last paragraph again last; they drift most because they are written first and in a hurry.

Saying it when you hand the text over

Written style is only half the task. You still have to talk about the document you wrote, and those spoken lines go back to desu-masu, because now there is a person in front of you. These are the sentences you say when you email a draft, hand over a printed report, or ask a colleague which style your workplace prefers.

A likely reply when you ask about style is Kono shorui wa de aru chō de onegaishimasu, meaning please use dearu style for this document, or Shanai bunsho wa desu-masu desu, meaning in-house documents use desu-masu. Both are short, fast and easy to miss, so practise hearing them as much as saying your own question.

A short drill that fixes buntai for good

• Pick five sentences you already say fluently and write each one in all three styles.
• Rewrite one paragraph of a Japanese news article into desu-masu, then back again.
• Keep a diary in da style for a week; it trains plain endings without any politeness anxiety.
• Write one paragraph about your work in dearu style and count how many de aru you actually needed.
• Copy the connective table onto a card and force yourself to use three written connectives per paragraph.
• Before sending anything, do the last-two-characters scan; it takes under a minute.

After a week of this, the choice stops being a grammar question and becomes a reflex tied to the document type. You will open a blank page, notice that it is an email rather than a report, and your fingers will produce masu endings before you have consciously decided anything. That is the point at which buntai is learned.