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Using "to be," in any form, is considered passive. But, just to clarify... a passive voice is not necessarily incorrect. It is a style issue, and personal preference. Sometimes using a passive voice can make your writing unclear, but, for the most part, there is nothing wrong with it. That is, unless you are being graded, and your teacher says not to use it.
Peeps: THANK YOU! You have concisely cleared up a point of contention in our Fiction Writing Critique Group! Books advise writers to eschew Passive Voice in order to be published. There has been much discord about this in our Critique Group. We are indebted to you!
Passive voice is constructed with some form of the verb "to be" and a past participle. The passive verb, in other words, is always a compound. The passive verb in its corresponding active form is always a transitive verb, that is, a verb that takes an object. In the passive formation, that object becomes the subject of the verb. Ex: Hamlet killed Laertes. Laertes was killed by Hamlet. Unless a verb is a transitive verb, it cannot be converted to the passive. An intransitive verb (verb that does not take an object) cannot be converted to the passive. A linking verb cannot be converted to the passive. If the verb is simply some form of "to be" on its own, then the verb is being used either as a linking verb, linking a noun or adjective phrase back to the subject, or the verb is followed by an adverb phrase. I am using "phrase" here in the larger sense: what follows the verb may be a single word, a grammatical phrase, or an entire clause. Exs. Hamlet was indecisive. Hamlet was the prince. Hamlet was here. These are the three basic sentence patterns for the verb "to be" used on its own. None of these is passive. Nor can they be made passive.
As for style, verbs are the lifeblood of the sentence, so it is true that excessive passive voice tends to eviscerate text. In the hands of novices, passive voice also often goes hand in glove with poorly constructed sentences. But certainly passive sentences can be every bit as crisp and clean as active sentences. It all depends upon the writer, and that writer's choices.
As for text that relies heavily on the use of the verb "to be" (even where these constructions are not passive), it depends on the writer. Some fine writers to favor that structure; others do not. It's purely a hallmark of style, in the hands of an accomplished writer. The writer who is still struggling to find her voice, and her style, should try to write successful sentences, shaping the text on the page to say exactly what she wants it to say, in the way she wants to say it. Certainly one can, and ought, to experiment with using strong verbs. But in the hands of a poor writer, just as many sentences go awry with strong verbs as do with the linking "to be."