what is an impersonal subject?
In linguistics, an impersonal verb is one that has no determinate subject. For example, in the sentence It rains, rain is an impersonal verb and the pronoun it does not refer to anything. In many languages the verb takes a third person singular inflection and often appears with an expletive subject. In the active voice, impersonal verbs can be used to express operation of nature, mental distress, and acts with no reference to the do-er.