Barrie England’s latest blog post is title “Grammar Basics: Active and Passive”.
Barrie says, “We can conclude from this that the English passive is formed by taking the object of the sentence as it appears in the active and placing it at the beginning of the passive sentence, thus making it the subject of the new sentence. We change the verb from the active to the passive by taking its past participle, painted in this case, and placing it after the appropriate tense of the primary auxiliary verb be. My portrait was painted by Picasso happens to contain, as we have seen, the Adverbial by Picasso. Such a constituent of the sentence is called the Agent or the Instrument, the latter because it tells us who (or sometimes what) was, yes, instrumental, in bringing about the action described. Note, though, that an Instrument is not always necessary in a passive sentence. We can say, for example, My house was broken into without saying who by, perhaps because we don’t know.”