When is used in grammar?

"Is" is a form of the verb "to be," and it has various uses in grammar depending on the context:

1. Present Tense:

* Statement of fact: "The sky is blue."

* Description: "This cake is delicious."

* Questions: "Are you ready?" "Is it raining?"

* Linking verb: "She is a doctor." (Connects the subject to a predicate nominative)

2. Auxiliary Verb:

* Present continuous tense: "He is working."

* Present perfect tense: "I have been working."

* Passive voice: "The door is opened."

3. Contractions:

* "It's" for "it is" or "it has"

* "He's" for "he is"

* "She's" for "she is"

4. Emphatic/Strong Form:

* "It is" used for emphasis: "It is important to be honest."

Here are some additional points:

* Subject-Verb Agreement: "Is" is used with singular subjects. For plural subjects, use "are."

* Formal vs. Informal: "Is" can be used in both formal and informal language. However, in very formal writing, "be" might be preferred in certain cases.

Remember, the specific use of "is" depends on the context of the sentence. By understanding these different roles, you can use "is" correctly in your writing and speech.