I want to know from a grammatical point of view why do we use be with will instead of using is and are. For example:

  • Jack will be skydiving tomorrow. Correct
  • Jack will is skydiving tomorrow. Incorrect

I also want to know why do we use is, are, was, and were instead of be in the present and past tenses. For example:

Present Tense

  • Jack is skydiving today. Correct
  • Jack be skydiving today. Incorrect

Past Tense

  • Jack was skydiving yesterday. Correct
  • Jack be skydiving yesterday. Incorrect

2 Answers 2


Every verb requires its own unique complementation. For example, "make" only takes a bare-infinitive: eg. "He made me cry"; "Keep" only takes a participle: eg. "He keeps crying"; etc.

"Will" belongs to a special category of verb, the modal verbs. Modal verbs (except "ought") allow only a bare-infinitive as a complement. Since the bare infinitive form of "is" and "are" is "be", it should be "will be", not "will is".

Present tense and past tense clauses are sometimes called finite clauses. Finite clauses require a main verb that is inflected for tense. So the bare-infintive (be), the past participle (been) and the present participle (being) are not possible.

  • Some other examples with 'will' would be 'will have', 'will go', etc. They are the infinitive stripped of the 'to'... thus, 'to be' 'to have', 'to go'. Jul 9, 2020 at 18:27

I'm not sure how one could answer that except to say, "because that's how the verb tenses are formed in English". Why do we say "is" instead of "fwacbar"? I suppose one could study the history of the language and say when the various words were invented, but that still wouldn't really tell you why. It would just tell you when.

Other languages that I know anything about have words or endings used to indicate verb tense and other grammatical constructions. Why does Latin use "-ba-" to indicate imperfect and "-bi-" to indicate future, and not the other way around? It just ... does.

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