Numerous Language Log posts by me, Mark Liberman, and Arnold Zwicky among others have been devoted to mocking people who denigrate the passive without being able to identify it (see this comprehensive list of Language Log posts about the passive). It is clear that some people think The bus blew up is in the passive; that The case took on racial overtones is in the passive; that Dr. Reuben deeply regrets that this happened is in the passive; and so on.
Our grumbling about how these people don’t know their passive from a hole in the ground has inspired many people to send us email asking for a clear and simple explanation of what a passive clause is. In this post I respond to those many requests. I’ll make it as clear and simple as I can, but it will be a 2500-word essay; I can’t make things simpler than they are. There is no hope of figuring out the meaning of grammatical terms from common sense, or by looking in a dictionary. Passive (like its opposite, active) is a technical term. Its use in syntax has nothing to do with lacking energy or initiative, or assuming a receptive and non-directive role. And the dictionary definitions are often utterly inadequate (Webster’s, for example, is simply hopeless on the grammatical sense of the word). I will try to explain things accurately, and also simply (though this is not for kids; I am writing this for grownups). If I fail, then of course the whole of your money will be refunded.
I won’t be talking about passive sentences or passive verbs: sentences are too big and verbs are too small. I’ll talk in terms of passive clauses. A clause consists, very roughly, of a verb plus all the appropriate things that go with that verb to complete a unit that can express a proposition, including all its optional extra modifiers. Sentences can contain numerous clauses, some passive and some not, some embedded inside others, so talking about passive sentences doesn’t make any sense. Nor does “passive construction” if you define it, as Webster’s does, as a type of expression “containing a passive verb form”. That would be far too vague even if English had passive verb forms (in reality, it doesn’t).