Using "Supposed to" in a prediction

Question

I have been arguing with my friends over the usage of 'supposed to' for quite a while now. It is my belief that 'supposed to' is used to describe the obligation of the subject. For example:

"I am supposed to go home early today."

"She was supposed to bring Nachos to the party."

However, my friend insists that he can use 'supposed to' to make a prediction. Here is the example he gave me.

"The house is supposed to be bought in the auction."

So can you please help me solve this grammatical conundrum and give an example of the proper usage of 'supposed to' in a prediction?

Answer 1

There are two different (but closely related) senses of to be supposed to involved here. Almost exactly the same thing happens with to be expected to, thus...

Sense A - prediction (what people think will happen)
1: The sun is supposed to turn into a red giant in a few billion years
2: The election result is expected to be extremely close

Sense B - necessity, duty or obligation (what people think ought to happen, often morally speaking)
3: My Dad says I'm supposed to be home by midnight
4: Judges are supposed to be politically impartial (I wish! :)

So OP's friend is perfectly correct in citing his "house sale" example (it's generally assumed that the house will be bought at auction - but no implication that this is somehow the morally or legally "correct" outcome).

---

Note that the "duty, obligation" sense is equally natural with expect - so the speaker's dad in #3 above might well have said to his daughter I expect you [to be] home by midnight with exactly that implication. But this doesn't happen naturally with suppose (the daughter might understand things entirely differently in the unlikely event her father had said I suppose you'll be home by midnight).

---

TL;DR; The two different senses outlined here only really apply to the passive form with to be supposed to [do or be something], not "active" contexts. But with expect, both senses can occur in both active and passive constructions.

.

Answer 2

It helps to go back to the actual 'original' meaning here, to understand how these phrases work.

Suppose is a verb, and usually means either to think something likely, or to expect/require something - or both at once:

I suppose you want a lift to school?

This is a person indicating that they think it is likely that the other person wants a lift, and that they expect they are going to be asked for it.

I suppose they changed their minds.

This might be said by someone who was planning to meet someone and they didn't turn up. It means that they think it is likely that they changed their minds. If you suppose something in the past, you are assessing the likelihood of unknown past events; if you suppose something in the future, you are assessing what is likely to happen - you are making a prediction.

This plan supposes that the enemy will approach through the hills.

This means that the plan is based on the assumption or expectation - or even pre-condition - that the enemy will come a certain way.

You might relate this to the noun supposition, meaning an underlying assumption. You will come across suppose used in this way in maths and philosophy:

Suppose that the triangle ABC is right-angled at B. This means that...

Now, taking this basic meaning literally, when someone is supposed to do something, it means that it is assumed or predicted that they will do that thing. However, meaning has shifted. For example, to bowdlerise a famous film quote:

You were only supposed to blow the doors off!

That is not about a prediction in any normal sense. It is about what a person was instructed to do.

Of course, supposed has become more like an adjective that requires a prepositional phrase, now, but it all comes down to that verb meaning.

So, your friend's example:

The house is supposed to be bought in the auction.

This is the 'original' meaning of supposed, meaning that someone is assuming or thinking it likely that what will happen in the future is that the house will be bought in the auction. It's awkward phrasing, but it's okay. We'd usually talk about a house being sold in the passive voice, rather than it being bought, at least in British English. We would use bought in the active voice, or sold, depending on whether the subject is the buyer or the seller.

Your examples, however:

I am supposed to go home early today

She was supposed to bring nachos to the party

These use the drifted meaning of what is expected because it had been instructed or promised. You could argue that they are still about expectations/prediction/likelihood, because the fact you have been told to go home early means it is likely that you will go home early. The fact that she said she would bring nachos means it is likely that she will bring nachos. However, this sort of obligation expectation is easy to think of as a separate meaning, and people will still use it in cases of obligation where they don't expect a person to meet their obligation (including, quite often, parents who ask their kids to get home early).

Answer 3

All of the examples in the original post are correct.

The core meaning of "is supposed" is "someone expects" or "someone makes a supposition".

The "prediction" sense is closest to this core meaning.

The "obligation of the subject" sense is that "people are relying on the subject to" _________.