「〜するはずだった」「〜することになってる」を一発で言える be supposed to、使いこなしてる？

Here's a phrase that native English speakers use all the time, but it often gets skipped in textbooks: be supposed to. On the surface it looks simple, but it carries a feeling that other phrases just can't capture.

The core idea is this: something was expected, planned, or agreed upon — and you're pointing to that expectation. Think of it as a gentle way of saying, "That's the rule" or "That was the plan." For example, "You're supposed to turn off your phone in the cinema." It's not a harsh rule — it's just what everyone understands to be correct.

Now here's the part that makes learners go "Oh!" You can use it in the past tense to talk about something that should have happened but didn't. "The train was supposed to arrive at 8, but it was 30 minutes late." That small word "was" changes the whole meaning — now you're expressing a gap between the plan and reality. Japanese speakers often love this because it feels close to 「〜するはずだったのに」.

You'll also hear it used for rumors or things people generally believe: "This café is supposed to have amazing cheesecake." Here, you're not 100% sure — you're passing along what you've heard.

One thing to keep in mind: be supposed to is softer than must or have to. It's not about your personal will — it's about an outside expectation. So next time a plan falls apart, don't just say "I couldn't do it." Try: "I was supposed to go, but something came up." That one sentence sounds natural, polite, and totally real-world English.