Simple Future has two different forms in English: "will" and "be going to." Although the two forms can sometimes be used interchangeably, they often express two very different meanings. These different meanings might seem too abstract at first, but with time and practice, the differences will become clear. Both "will" and "be going to" refer to a specific time in the future.
[will + verb]
FORM Be Going To
[am/is/are + going to + verb]
USE 1 "Will" to Express a Voluntary Action
"Will" often suggests that a speaker will do something voluntarily. A voluntary action is one the speaker offers to do for someone else. Often, we use "will" to respond to someone else's complaint or request for help. We also use "will" when we request that someone help us or volunteer to do something for us. Similarly, we use "will not" or "won't" when we refuse to voluntarily do something.
USE 2 "Will" to Express a Promise
"Will" is usually used in promises.
USE 3 "Be going to" to Express a Plan
"Be going to" expresses that something is a plan. It expresses the idea that a person intends to do something in the future. It does not matter whether the plan is realistic or not.
USE 4 "Will" or "Be Going to" to Express a Prediction
Both "will" and "be going to" can express the idea of a general prediction about the future. Predictions are guesses about what might happen in the future. In "prediction" sentences, the subject usually has little control over the future and therefore USES 1-3 do not apply. In the following examples, there is no difference in meaning.
In the Simple Future, it is not always clear which USE the speaker has in mind. Often, there is more than one way to interpret a sentence's meaning.
No Future in Time Clauses
Like all future forms, the Simple Future cannot be used in clauses beginning with time expressions such as: when, while, before, after, by the time, as soon as, if, unless, etc. Instead of Simple Future, Simple Present is used.
The examples below show the placement for grammar adverbs such as: always, only, never, ever, still, just, etc.
ACTIVE / PASSIVE