We have learned that both shall and will can be used to give and ask for information about the future. They can also be used to express ideas such as requests, offers, orders, threats and promises.
In these cases, will generally expresses willingness, wishes or strong intentions. Shall expresses obligation.
- ‘There is the door bell.’ ‘I will go.’
- If he does that again, I will break his neck!
- ‘You can have it for $10.’ ‘OK, I will buy it.’
Note that we do not use shall to talk about willingness or intention. Simple present tenses are also not used to announce decisions.
- I think I will go home. (NOT I think I go home.)
Will not or won’t is used to refuse, or to talk about refusals.
- I won’t go.
- He won’t do it.
Asking for instructions and decisions
Questions with shall I or shall we are used to ask for instructions, to offer services and to make suggestions. Will is not used to express these meanings.
- Shall I open the window?
- Shall I get you a cup of coffee?
- What shall we do?
- Shall I go?
In legal documents shall is often used with third-person subjects to talk about obligations and duties.
- The seller shall be responsible for paying the success fee.