57 Be To + Infinitive: Pre-Conditions

We use be to + infinitive when we discuss official arrangements, orders or official instructions.

We also use it when we are expecting something to happen (for Pre-conditions).

For Pre-Conditions we use if clause which is followed by be to + infinitive.

The structure is as follows:
If clause + be to + infinitive + second clause.

• If we are to been in Paris tomorrow, we should buy a direct flight.
• You must buy a helmet if you are to ride a motorbike.
• If we are to catch the inter-city bus, we should leave now.

As we want to talk about a Pre-Condition we use this structure with if-clause. It is common to see be to + infinitive structure in if clause sentences.