"be to do" versus "have to do"

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What is the difference between be to do and have to do?

I googled it and searched for other options as well though I couldn't figure out the differences.

Examples:

  1. I am to do these things.
  2. I have to do these things.

Ideal

Posted 2014-07-31T05:37:27.573

Reputation: 151

Answers

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"Have to" expresses obligation, while "be to" is usually about arrangements, giving orders or instructions. It is used in formal contexts. You can find more information on it here and here.

If it expresses prohibition (an order not to do something), then "be to" would be close to "be allowed to, can't", and of course "don't have to" has a completely different meaning:

You are not to leave without permission.

When used for arrangements, scheduled events, it is close to "be going to".

The Prime Minister is to make a further visit to Devon next week.

You can also use "have to" here, it would mean that he is obliged to, based on the arrangements that have been made, while "is to" simply informs us that it has been scheduled.

Only "be to" can be used in an if-clause:

If you were to bake a cake, I would eat it. (= If you baked a cake, I would eat it.)

When giving orders you can use both:

You are to/have to come at 9!

You're to/have to sit in the corner and keep quiet.

You are to/have to carry your passport at all times.

Often "have to" means that there is a rule and what the speaker says is based on that rule, he is only reporting the order, not issuing it. In the last sentence, for example, it is the law.

In a sentence such as this:

All students are to/have to take a written exam at the end of this course!

without any other context we have no idea whether this is a written order, issued by the principal, or a teacher informing the students of that order. The good news is that most of the time "have to" and "be to" are interchangeable when referring to orders.

In the two sentences you have given, the second means that someone told you to do it. It is external obligation. The first sentence could mean 2 things: 1) It is your turn to do it (scheduled) or 2) someone ordered you to do it (obligation).

fluffy

Posted 2014-07-31T05:37:27.573

Reputation: 2 800

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I can't really articulate why, but I think "I am to do these things" suggests that someone has ordered or instructed you to do them. Perhaps it comes from the fact that "You are to do this" seems to be a standard phrase in military orders. On the other hand, "I have to do these things" just means that for some reason it is necessary for you to do them.

If the sink is full of dirty dishes and I decide this needs to be taken care of, I would say "I have to wash the dishes."

If my family is getting ready for a party and everyone has been assigned chores, I might say "I am to wash the dishes."

Nate Eldredge

Posted 2014-07-31T05:37:27.573

Reputation: 2 133

1

"to be to do" is elliptic. A past participle after to be has been dropped. Possible is you are ordered/demanded/required/destined/expected/supposed etc to do. http://www.macmillandictionary.com/dictionary/british/be-to-do-something

rogermue

Posted 2014-07-31T05:37:27.573

Reputation: 8 304