Why can't I say as this on this situation?
I'm studying "English Grammar in Use".
At Unit23, this textbook says "We use will to announce a new decision", and "We use (be) going to when we have already decided to do something".
In the Exercise of the Unit, there's a question below.
---
It's a nice day, so you've decided to take a walk. Just before you go, you say:
The weather's too nice to stay in. (I / take) a walk.
---
"I'll take a walk" is wrong answer and "I'm going to take a walk" is only right in this textbook.
However, it's a new decision "to take a walk" because I decided it just after seeing the nice weather. Why can't I say "I'll take a walk" on this situation?
回答
This is not a piece of advice to you I'm talking to myself for my practice of writing skills. I think your thought is right. but i'm not so strong to be able to bite the printed such as textbook. I've searched on the web but I couldn't find any more than your explanation. I'll post comment with two sites for reference. I suppose you're no longer an advisee (who receives advice), already you've come to be an adviser(who gives advice).
The Difference Between “Will” and “Going To”.
https://languagetool.org/insights/post/will-vs-going-to/.
https://www.grammar.cl/Notes/Future_Will_vs_Going.htm.