As is evident from the name continuous they are those tenses which show continuity of verbal action. Here we have to look for auxiliary and the form of the main verb that have the same function to show continuity of verbal action.
Auxiliaries that show continuity of verbal action
As explained earlier present form of auxiliary verbs are used in present continuous tense whereas past form is used in past continuous tense. If you cast your mind back in the chapter of verb we have explained that first form is named as present and used in present time situation and second form is past and used likewise in past time situations.
As we have already mentioned that there is no form of the verb which stands for future, so we have to use modal operators (will and shall) along with be in continuous tenses. It is important to know that the verb be is the same verb that is used in the present and past continuous tenses, since all are be-forms. Shall is used with first person pronouns (I and we) whereas with all other subject we shall use will. And in case of showing emphasis they are interchanged.
Shall is used to express determination, compulsion, certainty and uncertain futurity. For more uses of shall visit previous chapter of simple tenses.
Form of the main verb that show continuity of verbal action
In continuous tenses we have to use the form of the verb with the same function (continuity of verbal action), and for this purpose we have to use present participle form (–ing).
Future continuous is not necessarily future time situation; rather it is sometimes present, expressing a sort of conjecture or guess. Now consider the following sentences of future continuous.
The sentence gives an impression of futurity (future time situation). And if we add adjunct [tomorrow] with it, like,
Now it is certainly future time situation, but there are certain adjuncts which can pull it back to present despite the fact that auxiliary and main verb remains intact, like,
In short we can’t say that
convert sentence into future in all cases.