[Grammar] Oh, I work as usual.

[Son Ho]

Hi teachers!
I found a grammar point in A Practical English Grammar by A.J.Thomson and A.V.Martinent. Why can't we use the simple present as a habitual action in (e)? If we can, please tell me the real differences between them which are really confusing.

215. Examples of various future forms:
A. Imagine that we ask five people about their plans for the following Saturday. We say:
What are you doing/ going to do on Saturday?

(e) Bill always has to work on Saturdays; so he will say:
Oh, I'll be working as usual. (No other form would give this exact meaning)

 

[jutfrank]

Why can't we use the simple present as a habitual action in (e)?

Because it does not express a habitual action. Bill is talking about a specific time in the future.

 

[Tdol]

The simple present for habitual actions would be:

I work on Saturdays.

He's talking about this Saturday, even though it is the same as every Saturday.