Understanding and Using Modal Verbs: Understanding and Using Modal Verbs (#27)

The English modal verbs are often challenging for learners
of English. This happens for many reasons, including both
grammar and meaning.

In this Hint, we'll look at differences between the use of will
and be going to when talking or writing about future events.

One use for the modal auxiliary will (and also for be going to)
is in showing someone's predictions about the future--things
that someone speaks or writes about before they actually happen.
Another use for will (but not be going to) is in showing
willingness or volition--being agreeable to the idea of doing
something. When will is used in this way, it can refer to either
present or future time.

When someone speaks or writes about an event in the future,
maybe that event was planned in the past and maybe it wasn't.
If the event was planned in the past, be going to, but not will,
is used. If the event was not planned in the past, either will or
be going to may be used.

Examples:

(B has already made plans to go to bed soon, so she/he
uses be going to, not will.)

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(B has already made plans to visit friends in San Francisco,
so she/he uses be going to, not will.)

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(Because A assumes that B and her/his friends have made plans
about what to do, A uses be going to in the question. Because
no plans have been made, B uses will in the answer--though
be going to is also possible.)

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(Because A isn't sure when B plans to return, she/he uses
will in the question--though be going to is also possible.
Because B has already made plans to return on the 16th,
B uses be going to in the answer.)

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Remember:

When no plans for the future have been made in the past,
either be going to or will may be used--because the future
event will be a prediction. When plans for the future have
been made, only be going to may be used.