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!
Other Properties of the Middle Voice
The middle voice has some other differences from passive voice. With the passive voice, you don’t have to mention the agent, although you can if you want to. With the middle voice, you can’t. A sentence like “Those spearheads didn’t cast very well by the blacksmith” is ungrammatical.
With the passive voice, you don’t have to mention the agent, although you can if you want to. With the middle voice, you can’t.
Second, middle-voice sentences usually include some adverbial meaning, negation, or a modal verb, or a combination of the three. “The spearheads didn’t cast very well” has both negation (“didn’t”) and an adverb phrase (“very well”). “The screw screwed in more easily than I thought it would” has the adverb phrase “more easily than I thought it would.”
Third, middle-voice sentences insinuate that the responsibility for the action is not with the agent, but with the patient. When the blacksmith said, “Those spearheads didn’t cast very well,” it sounds a bit like the bad casting was not the blacksmith’s fault; maybe it was some problem with the metal. A clearer example is “The screw screwed in easily.” The speaker isn’t saying that their own mastery of hand tools allowed them to screw in the screw. Instead, something about the inherent or designed properties of the screw made it possible. For this reason, they sometimes also go by a more-specific name: the dispositional middle voice. It was the disposition of the screw, something inherent to its nature, that made it easy to screw in.
This property is tied to the last one we’ll mention: Since middle-voice sentences are more about saying something about the qualities of their subject, they often don’t refer to a specific event. For example, “This history book reads like a novel,” “My car drives smoothly,” and “Squiggly doesn’t embarrass easily” are general statements, not about particular events. Possibly the most famous dispositional middle-voice sentence in the United States is from a TV commercial in the 1980s, which states that a certain brand of soup is “the soup that eats like a meal.”
However, not all middle-voice sentences are dispositional. For example, Steven’s sentences about spearheads and screws do refer to particular events. So do sentences such as “Your receipt is printing,” “The painting sold for $1.2 million,” and “Suddenly, the tablecloth blew away.”
As it turns out, middle-voice sentences are not the only kind of construction in which a verb that ordinarily takes a direct object doesn’t take one, and instead has a patient as its subject--and isn’t passive voice. English has two others.
One of them involves verbs that name actions that agents do to themselves or to each other. To put it another way, the subjects of these verbs are both agent and patient. For example, think about the verb “shave.” It can be used as an ordinary verb with a direct object, in a sentence such as “Fenster shaved his tail.” But it can also be used without a direct object, as in “Fenster shaved.” In that case, it means the same thing as “Fenster shaved himself.” For another example, the sentence “Squiggly and Aardvark hugged” means the same thing as “Squiggly and Aardvark hugged each other,” even though it doesn’t use the phrase “each other.” In these examples, the agent doing the shaving or hugging is also a patient, getting shaved or receiving a hug.
The other kind of patient-subject construction involves verbs such as “break,” “melt,” “boil,” “freeze,” “open,” “close,” “burn,” and many others. Let’s illustrate with the verb “burn”. You can definitely use “burn” with a direct object, in a sentence like “My roommate had burned the cookies.” You can also put it in the passive voice, as in “The cookies had been burned,” and your listeners will know you mean it didn’t just happen; someone or something did it. But you can also use it with a patient-subject, as in “The cookies had burned.” In this sentence, maybe there was an agent, or maybe the burning just happened. The speaker isn’t telling us. And as with dispositional middle-voice constructions, we can’t specify an agent. The sentence “The cookies had burned by my roommate” isn’t a possible sentence. These verbs go by several names, but the one that I find easiest to understand is “anticausative verbs.”
So all together, there are four kinds of patient-subject constructions in English, and only one of them is the actual passive voice! The other three are the verbs of reflexive or reciprocal action, as in “I dressed quickly” and “Where did Kim and Sandy meet?”; the anticausative verbs in sentences such as “The door opened” or “My tomatoes froze”; and the middle-voice sentences that kicked off this episode, such as “The spearheads didn’t cast well” and “My new boat handles like a dream.” We need a convenient name for these three kinds of constructions, so I’m going to use the acronym RAM: R for reflexive and reciprocal, A for anticausative, and M for middle voice.