We find to be to + Infinitive to discuss official arrangements, orders or official instructions.
This structure has both active form and passive form.
We use the active form when we are expecting something to happen (for pre-conditions).
For pre-conditions we use the if clause and to be to + Infinitive.
The structure is:
If-clause + to be to + infinitive + second clause
- If we are to be 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.
We usually use this structure with the if-clause if we want to talk about a pre-condition.