Thoughts very rarely translate into language in completely formed phrases. Sometimes it takes a stab or two to articulate what exactly it is you’re trying to say.
The opposite, however, is also true: Incomplete language can and often does imply perfectly complete ideas, and sometimes an incomplete phrase is the most natural way to express something. And Japanese is a language where this seems especially true.
One of the very first phrases students of the language learn is お名前は？ (O-namae wa?, “[What’s] your name?”) This is not a complete sentence grammatically. You can add 何ですか？ (Nan desu ka?, What is?) and complete the sentence, but it isn’t necessary; everyone in the conversation knows what’s being asked, so in the interest of economy, it gets left out.
This is also true of the casual quotative particle って (tte). Tte is used to tag quoted speech, and it’s easy to leave off the verb 言う (iu, say) when it’s unnecessary. For example, 来ないって (Konai-tte) is a perfectly good way to say “Ayaka says she isn’t coming.” Marvel for a moment at the efficiency of the Japanese language.
Feel free to use tte to report other more interesting information, such as カープが 勝ったら、ビールを奢ってくれるって (Kāpu ga kattara, biiru o ogotte kureru-tte, “[She/he says] she’ll/he’ll treat us to beers if the Carp [Hiroshima’s baseball team] win”).
You can take advantage of と (to) to make deeper inquiries incompletely. For example, if your professor is lecturing you on international relations and mentions that there could be 問題 (mondai, problems) with the ratification of the Trans-Pacific Partnership trade deal, you can ask for further clarification with the incomplete phrase 問題とおっしゃいますと…? (Mondai to osshaimasu to … ?, “[What do you mean] when you say problems?”). What’s left off in this case is something like 詳しくどういう問題ですか？ (Kuwashiku dō iu mondai desu ka?, “What kind of problems in particular?”).
Incomplete sentences are also useful if you fancy modulating your tone. Want to sound like an ornery teenager? Make use of the explanatory conjunctive particle し (shi). If your mother (or a friend) asks 節子を連れてデートしてみたらどうですか (Setsuko o tsurete dēto shite mitara dō desu ka, “Why don’t you take Setsuko out on a date?”), just respond with 全然 タイプじゃないしさ (Zenzen taipu janai shi sa, ” ‘Cuz she isn’t my type at all”).
If you’re going for circumspect librarian, opt for ので (no de) or the shortened んで (nde) when making explanations. If, say, someone is talking during the recording of a broadcast of some kind, you could nudge them and say ただいま録音 していますので … (Tadaima rokuon shite imasu no de …, “We’re currently recording at the moment, so …”). Implied is 静かにしてください (Shizuka ni shite kudasai, “Please be quiet”). No de is a great way to ask someone to cut out whatever it is they’re doing without having to explicitly tell them to stop. After they’ve complied, you can soften the tone by adding はい、 申し訳ありません (Hai, mōshiwake arimasen, “I’m terribly sorry”).
One of the most casual ways to throw around incomplete sentences is by using で (de) and て (te) as gerund forms of verbs, nouns or adjectives. Both act as incomplete ends to sentences that let people in a conversation toss phrases back and forth.
For example, a friend is telling you about a recent shopping trip: 目黒に行って、ちょっとぶらぶらして、めちゃおいしいうなぎを 食べて (Meguro ni itte, chotto burabura shite, mecha oishii unagi o tabete, “I went to Meguro, walked around a bit, ate some amazingly delicious eel …”). He pauses here as he recalls the divine flavor of the eel, and you spur him on with a simple inquisitive で? (De?, “And then?”)
He continues: 自分で行って食べてみないとね (Jibun de itte tabete minai to ne, “You really should go and try it yourself.”) Here he uses the incomplete particle to to suggest that it would be もったいない (mottainai, a shame) or 残念 (zannen, unfortunate) if you don’t take the opportunity to try it yourself.
You might reply, 行きたいんだけど (Ikitain da kedo, “I’d like to but …”), and the unspoken ellipsis at the end of the sentence might be all you need to suggest it’s beyond your budget at the moment. Once again, an incomplete sentence comes in handy in a delicate situation.
And we shouldn’t forget 一体 (ittai) and なんて (nante), very effective ways to express exasperation, shock or disbelief using a grammatically incomplete phrase.
Generally, ittai gets attached to question words such as 一体誰が… (Ittai dare ga …, “Who the …?”) or 一体どこに… (Ittai doko ni …, “Where the…?”) to express a frustration with someone doing something dumb or unbelievable, or an inability to find something you’ve misplaced.
But sometimes ittai on its own is all you need. A Facebook friend recently made use of it for a little self-deprecating humor in his status update: こんな 時間にヒレカツ丼を食ってるオレは一体 … (Konna jikan ni hirekatsu-don o kutteru ore wa ittai …, “What the heck [am I doing/thinking] eating fried pork fillets at this [late an] hour?”)
And with nante, all you need to do is attach it onto the end of any ridiculous action to express your incredulity. Use the word まさか (masaka) at the beginning as a sort of emphasizer. For example, if you’re responding to current events, you can say まさかトランプが共和党大統領候補者になるなんて… (Masaka Toranpu ga kyōwatō daitōryō kōhosha ni naru nante …, “[I never thought] Trump would become the Republican presidential candidate …”). Left off here is 思わなかった (omowanakatta, I didn’t think).
Being incomplete is something that can actually make you appear more complete as a Japanese speaker. Some scholars report that Japanese leave their sentences incomplete 25 to 50 percent of the time! These are just a few examples, so be sure to listen closely to complete your collection of incomplete sentences.