The major constructions used to express future time reference in English can be briefly described as follows:
1. The going to future is composed of be + go participle) + to + infinitive, e.g.,
I'm going to meet him at the station
This construction implies that present circumstances to some extent determine or influence the predicted future event. 'Keith human subjects the going to future can indicate intention (as in the example above), and with both human and non-human subjects it can indicate that the future event or the sequence of events leading to it is already considered underway, e.g.:
I just know I am going to fail the exam.
That old jalopy is going to break down any minute.
2. The will/shall future is composed of wi11 or shall + infinitive, e.g.:
I'll meet you at the station.
Shall is restricted to first person subjects and British English. With first person subjects there is often an implication of intention, which differs from that of going to in that the intention is more spontaneous or concurrent with the moment of speaking rather than the result of a previous decision, e.g.:
"My train leaves in fifteen minutes." "Oh? I'll drive you to the station, then." (spontaneous decision)
versus
"My train leaves in fifteen minutes. "Yes, I know. I'm going to drive you to the station, so there's no hurry." (previous decision)
3. The present progressive, composed of be + -ing participle, has future meaning when it refers to an event that is expected according to an already existing plan or arrangement. Since it implies 'arrangement', this form can only occur with verbs involving human agency, e.g.:
I am meeting him at the station tomorrow morning.
*It is raining tomorrow morning.
4. The simple present is used with future time reference in temporal and if clauses, and when the future event is regarded as absolutely certain, i.e. scheduled according to the calendar or a timetable, e.g.:
I'll be at the station when you arrive (temporal clause)
If you arrive early you'll have to wait for me (if-clause)
The train arrives at 5:30 tomorrow morning (certain future)
In addition, the simple present of modal and other auxiliary verb constructions also have future meaning, e.g.:
You can see him tomorrow.
He is supposed bound/(un)likely/about/expected to speak.
He is on the point of speaking.
He is to speak tomorrow.
5. The future progressive is composed of will/shall + be + -ing participle. It can indicate a temporary future state or activity during which another event takes place, eg.:
I will be washing the car when you arrive.
It can also refer to a future event that is planned, but less definite or certain than in the case of the present progressive or simple present. Will/shall in this construction does not carry the potential overtones of volition as in the simple wi11/shall future. For example,
I'll be visiting my parents next weekend.
expresses a planned or expected event, but one which is still considered less certain to occur than in
I'm visiting my parents next weekend.
or
I visit my parents next weekend.
and there is no implication of the speaker's will or decision to go, as in
I'm going to visit my parents next weekend.
Rule: The simple present expresses future time reference only in temporal and conditional clauses, or when referring to the calendar, timetables, etc.
Examples of errors:
The use of the simple present tense to express future time is much less frequent and more restricted than in German. It is found in newspaper headlines, timetables, travel itineraries, statements about the calendar, and other contexts where the future event or state is seen as a certainty, fixed by some external authority or plan--that is" not subject to change by the speaker's or someone else's will. It is almost always accompanied by a time adverbial, e.g.:
The train leaves at five o'clock.
President leaves for Moscow tomorrow (newspaper headline)
Next Monday is Memorial Day.
Future events that are logically subject to doubt cannot be expressed in this way in English, though they can be in German:
*It rains tomorrow.
*I'm absolutely certain that John passes his exam next week.
Es regnet morgen.
Ich bin absolut sicher daß John seine Prüfung nächste Woche besteht.
Hope allows for an exception to this rule, in that the following subordinate clause may use either a future tense form or the simple present:
I hope John will pass/passes his exam next week.
If there is a long parenthetical interruption between hope and the subordinate clause, however--as in (10)-the general rule applies and the simple present is distinctly less likely.
The question of whether an event (or a state) belongs to the future or the present time is not always a simple one. Now, for example, normally means 'at the present time', but the time reference of give and stop in (2) and (1) is not 'now' but the immediate future: the giving and the stopping is not taking place at the time of speaking, but will follow immediately. This seeming contradiction could be reconciled by interpreting now in (2) and(l) as meaning something like: 'Now is the time period during which I will....' Alternatively, one could think of this use of now as intermediate between the' temporal meaning 'at present' and what its use in a sentence like the following as a transitional conjunction, i.e. with no temporal meaning at all, as in
I used to have a dog named Crackers. Now Crackers was a rather temperamental beast...
Most of the sentences above would be acceptable with either the will/shall (only will in American English) or the be going to future, although the latter form carries with it certain implications of meaning that are inappropriate in some contexts (cf. Edmondson et al. 1977:156-161; Leech 1971:§91-96; Nehls 1978: §3.3). One such implication, when the subject of the verb is also the agent or cause of the action denoted by the verb, is that of intention or previous resolution on the part of the subject. Thus, in (l)-(5), I am going to would connote that the speaker has already thought about what he will do and has resolved to do it; I'll connotes a less deliberate action, a more neutral prediction or statement about a future event. For this reason. be going to in (7) would sound odd, 'since it implies intention, whereas the first part of the sentence refers only to a possibility.
In (8), if they are going to give you the money would pose a question more about the intention of the parents than about the future event per se. With non-agentive subjects (and non-action verbs), be going to implies, as Leech (l971:§93) puts it, that "The train of events leading to the future happening is already under way". I think Rachel is going to believe Daniel (cf. (9)) implies an inevitability about the future event that is absent with will. In (10) is going to get sounds a bit odd, since one does not ordinarily hope for things that are inevitable or already on the way. These two different senses of the be going to construction can become confused in sentences like
I think I'm going to be sick.
I think I'll be sick.
where be going to, in the first sentence, implies inevitability, but in the second sentence will--which is normally the neutral form--implies a deliberate act. What is really being contrasted in these two sentences, however, is not be going to and will but two different meanings of be sick: 'become sick' versus 'act (or force oneself) to be sick'. If we contrast two sentences where the meaning of the verbs is the same, the difference between the two constructions becomes clear again:
I think I'll watch TV for a while (neutral)
I think I'm going to watch TV for a while (i.e. 'I've thought about it and this is what I've decided'--indicates intention)
I think it'll rain tomorrow (neutral)
I think it's going to rain tomorrow (i.e. 'present factors--weather report, clouds, barometer reading, etc.--indicate that it will rain tomorrow'--indicates inevitability)
If the inevitability of the future event is clear from context, as Nehls (1971:39) points out, either will or be going to is possible:
Look at those clouds. It will/is going to rain in a minute.
The will/shall future (cf. (12)) is not used in temporal or conditional clauses. Temporal clauses are those introduced by when(ever), before, after, as (soon as),, once, till, until:
When he arrives, he'll tell us all about it.
Before you go to bed, brush your teeth.
I'll keep asking you until you tell me.
The be going to future is not normally used in such contexts, either, although we have to allow for sentences such as:
Whenever it's going to rain, I feel a pain in my big toe.
He yelled at me until I was going to slug him, but just then my brother came in.
Be going to still retains enough of its original present time meaning to occur in such contexts, and confirms Edmondson's et al. (1977:157) description of the basic meaning of this tense form:
There currently obtains a state of affairs, which is liable to change (of limited duration), and ... which in the normal course of events will necessarily lead to P [i.e. proposition--the future event] becoming the case.