The simple present is often used to express habitual actions referring to no particular span of time, such as in He walks to school' The simple present is often employed in newspaper headlines instead of the present perfect:
It is employed in if clauses referring to the future:
It is used when a planned event is described along with a time in the future:
It is used with stative verbs in referring to states (unchanging situations) that exist in the present:
It can also be used when making a citation:
In a yes-no question, the simple present becomes compound, employing the auxiliary do:
When a question word starts a sentence, do is included if the question word is not the subject of the sentence:
But when the question word is the subject of the sentence, the simple form is retained:.
The continuous (progressive) verb form in English conveys that an action is ongoing, as in "She is running right now". So for evolving situations in the present, the simple present form is not used. In contrast, the simple present is used for present situations that are not evolving, as in "I know that", which cannot be rendered as "I am knowing that."
* English Grammar in Use 7th PRINTING 1998 by R.Murphy-2nd edition-ISBN: 0 521 43681 8
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