In my book, both forms mentioned in the title have been defined as:
Be to + infinitive is commonly used in news reports to talk about events that are likely to happen in the future:
- Police officers are to visit every home in the area.
We use be about to + infinitive mainly in conversation to say that something will (not) happen in the very near future:
- We're about to eat. Do you want to join us?
The book doesn't explain the difference (I assume there's no difference when we say something is likely to happen and something will happen). Regardless of the different usage between be to is used in news reports and be about to is used in conversation, are those forms have different meaning? Or is it just the formality usage that differs them? Meaning be+to is used in formal situation?
The reason I'm confuse, because the book, in the previous unit(chapter) also says that will can be used to state that something is likely to happen. [E.g. It will rain]. That's why I'm confused between those definitions.