Passive Voice : Many people think any sentence that has a verb like is, was, or were is passive voice, but that's not true.
A passive sentence is when the object of the sentence gets promoted to the subject position.
Here's an active sentence:
I mailed the letter.
I is the subject, is taking the action, and is in the subject position; and the letter is the object, is being acted on, and is in the standard object position.
If you flip it around and promote the object—the letter—to the subject position before the verb, you get a passive sentence:
The letter was mailed by me.
All passive sentences have a form of the verb to be such as was or were or is in them, but not all sentences that have those verbs are passive.
Sometimes people miss the point that the sentence must have an object (the receiver of the action) to be able to be phrased in the passive voice. If a sentence doesn't have an object, you can't move words around to make it passive.
In a passive voice sentence, that object—the receiver of the action, the letter in this case—is in the subject position in the sentence.
The letter was mailed by me.
Sometimes a sentence will leave off the “by me” part, and you’ll end up with something like this:
The letter was mailed.
Notice that the receiver of the action is still in the subject position. If you’re trying to figure out whether a sentence is in the passive voice, one trick is to see if you can add ‘by so-an-so” to the end. If you can, it’s in passive voice.
