be supposed to(〜することになっている)Be Supposed To: What's Meant to Happen
助動詞 / Modal Verbs
be supposed to は「予定・規則・期待のうえでは〜することになっている」。過去形 was supposed to になると、多くの場合「〜のはずだった(のに実際は違った)」という含みがセットで付きます(文脈次第で消えることもあります)。助動詞ではありませんが、助動詞並みに毎日使われる準レギュラーです。
Be supposed to means "according to the plan, the rules, or everyone's expectations, this is what happens." Shift it to the past — was supposed to — and "but it didn't" usually comes along (context can cancel it). Not technically a modal, but it works modal-grade shifts every single day.
第3の義務: 「取り決め」の圧
The Third Kind of Pressure: Arrangements
must は内心から、have to は事情から。be supposed to は「まわりの取り決め・期待」から来る、いちばん柔らかい圧です。破られる可能性が最初から織り込まれているのがミソで、だからこそ「ことになっている(けど、どうかな)」というニュアンスが出せます。評判を伝える用法もあります: This movie is supposed to be good.(この映画、評判いいらしいよ)。
Must presses from inside, have to from circumstances, and be supposed to from the web of arrangements and expectations around you. It's the gentlest of the three, because the possibility of the plan failing is baked in: "that's the arrangement… in theory." It also carries reputation: This movie is supposed to be good — that's what everyone says.
予定・規則・評判Plans, rules, reputations
I'm supposed to be at work by nine.
9時までに出社することになっている。
規則・取り決めの圧。The pressure of the arrangement.
It was supposed to rain today.
今日は雨のはずだったんだけど。
予報どおりにならなかった含みが、たいてい付く。The forecast said so — and reality didn't comply.
This restaurant is supposed to be amazing.
この店、すごく評判いいらしいよ。
評判・伝聞の用法。自分ではまだ確かめていない。Reputation mode — you haven't verified it yourself.
have to
事情として必須。逃げ場がない。Circumstances demand it — no way out.
I have to finish this tonight.
今夜中にこれを終えないといけない。
be supposed to
取り決め上そうなっている。破られうる。That's the arrangement — which can fail.
I'm supposed to finish this tonight, but I'm exhausted.
今夜中に終える約束なんだけど、もうへとへとで。
よくある間違い / Common Mistake
×It is supposed to rain yesterday.
昨日は雨のはずだった。(のつもりで)
○It was supposed to rain yesterday.
昨日は雨のはずだった。
時制は be 動詞が担います。過去の「はずだった」は was / were supposed to。supposed の形は変わらないので、be の活用だけ意識すれば大丈夫です。
The be carries the tense. Past "was meant to" = was/were supposed to. Supposed itself never changes — just conjugate the be.
What's that supposed to mean?それ、どういう意味?(挑発への返し)「その発言は何を意味することになってるの?」という抗議の定番。"What meaning is that remark arranged to carry?" — the standard pushback.
I'm not supposed to ...本当は〜しちゃいけないことになってる規則を破りかけている自覚の言い方。I'm not supposed to tell you this, but ...(内緒なんだけど…)Rule-bending with a wink: I'm not supposed to tell you this, but …
You're not supposed to be here.ここにいちゃだめでしょ。規則違反の指摘。映画の潜入シーンの定番台詞でもある。Calling out a rule-breaker — and a movie-scene staple.
supposed to be the best最高との評判評判用法+最上級。おすすめの又聞き紹介に。Reputation mode meets the superlative — secondhand raves.
まとめ / Summary
be supposed to =取り決め・期待の圧。must / have to より柔らかい。Be supposed to: pressure from arrangements — gentler than must or have to.
was supposed to には「実際は違った」が標準装備。Was supposed to has "but it didn't happen" built in.
評判の用法もある(is supposed to be good =評判がいい)。It also reports reputation: is supposed to be good.
時制は be が担う(is → was)。The be carries the tense: is → was.