* Verb: This is the most common use of "be." It is the auxiliary verb used to form the present tense ("I am," "you are," "he/she/it is") and the past tense ("I was," "you were," "he/she/it was") of many verbs. For example: "I am happy." "They were late."
* Verb: "Be" can also be used as the main verb in sentences that express existence, identity, or state of being. For example: "The sky is blue." "She is a doctor."
* Noun: "Be" can be a noun, although this is rare. It often functions as a singular noun referring to the state of existence or being. For example: "To be or not to be, that is the question."
Therefore, the part of speech of "be" is determined by its function in the sentence.