A sentence such as ""The screw screwed in more easily than I thought it would," isn't in passive voice. It's in something called middle voice!
I got a comment on YouTube from a listener named Steven, who asked about verbs like the ones in this following sentence: "The screw screwed in more easily than I thought it would." Clearly, the screw didn’t screw itself in. The person who uttered the sentence screwed it in. A similar sentence came from a blacksmith he was talking with, who had cast some spearheads--that is, he had shaped them by pouring molten metal into a mold. The blacksmith wasn’t happy with how the spearheads had turned out, and he said, “Those spearheads didn't cast very well.” As Steven pointed out, “[T]he spearheads couldn't have cast themselves.” You might think phrasing a sentence this way would lead to total confusion, but it doesn’t. How is that possible? Steven wondered if this grammatical phenomenon has a name.
In fact, there is a name for it. It’s usually called the middle voice, although if you want a more jargony name, you might prefer “mediopassive construction.” We’ve talked about active voice and passive voice in other episodes, but how does middle voice fit into the picture? To see how it does, we need to start with a recap of what active and passive voice are.
Passive in Meaning, but Active in Form
In a typical active-voice sentence, the verb’s subject is the agent--the person or thing that performs the action. For example, “The blacksmith cast the spearheads” is in the active voice. The subject of the verb “cast” is “The blacksmith,” and the blacksmith is the one who did the casting. Depending on what verb you choose, there might also be a patient role, for the person or thing that undergoes the action. In the sentence “The blacksmith cast the spearheads,” the patient is the direct object, “the spearheads,” since they’re what underwent the casting process.
On the other hand, when a sentence is in the passive voice, the verb’s subject is the patient. The sentence “The spearheads were cast” is in the passive voice, and “the spearheads” is now the subject. As for the agent, it doesn’t have to be expressed. If you want to express it, you can do it by using the word “by”; for example, “The spearheads were cast by the blacksmith.” But here’s an important point: Whether you express the agent or not, there has to be one. In other words, if you say, “The spearheads were cast,” you’re implicitly saying that someone or something cast them; it didn’t just happen on its own. We know this is true, because a sentence like “The spearheads were cast, but no one cast them” is a contradiction.
So now let’s talk about “Those spearheads didn’t cast very well.” Once again, the patient is the subject, so this sentence is similar to passive voice in that way. Also, there was definitely an agent--the blacksmith--even though we’re not saying so explicitly. So that makes two things that this sentence has in common with the sentence in the passive voice.
However, in form, “The spearheads didn’t cast well” does not look like passive voice. In English, a verb phrase in the passive voice typically consists of some form of the verb “be,” and a past participle. For example, in the passive-voice sentence “The spearheads were cast,” we have “were,” which is a past-tense form of “be,” and the past participle “cast”—“were cast.” We don’t have any of that in the sentence “Those spearheads didn’t cast very well.” We just have the ordinary, active-voice, negated verb phrase “didn’t cast.”