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!
Middle Voice in Other Languages
Not all languages express RAM meanings the way English does, but interestingly, these meanings tend to cluster together in different languages. A paper by Artemis Alexiadou and Edit Doron, published in 2012, divides languages into three groups. The group that includes English lets active-voice forms express RAM meanings. Another group, which includes Classical Greek, modern Hebrew, standard Arabic, and an African language called Fula, have an active voice and a passive voice, and also a third set of verb forms, which is used for RAM meanings. This third set, you may have guessed, is called the middle voice. This group of languages also includes some of the Romance languages, such as Spanish and French. If you know some Spanish, you may have noticed that a sentence such as Se habla español, which is usually translated as “Spanish is spoken,” actually seems to mean “Spanish speaks itself”! That’s because the same verb forms, namely the reflexive ones, are used both for actual reflexive meanings and for patient-subject meanings where the agent is unknown.
The third group of languages that Alexiadou and Doron identify includes languages such as Amharic and Modern Greek. These languages don’t have a passive voice at all--instead, they have an active voice and a voice that covers all the situations where a patient is a subject. So for that reason the non-active voice in these languages is often called the medio-passive.
Middle Voice Everywhere
According to one study, middle voice is on the rise in English, with an especially big increase in frequency and variety during the twentieth century. Once you start thinking about the middle voice in English, you’ll start to notice it everywhere. In fact, and this is a true story, in a single day while I was writing this script, I noticed two of them in a magazine article about the airline industry. One sentence said that deregulation “made it easier for new carriers to launch,” with the patient “new carriers” as its subject. The other said that the galleys were the places “where we enter and exit the plane, [and] where the drink carts stow.” The drink carts don’t stow themselves; the flight attendants stow them. Mere hours later, an air-conditioner technician told me as he wrote up the paperwork for a service call, “The bill will be sending this week.” A couple more hours later, I downloaded some updated software for a handheld device, and a message on my screen said, “Your file is downloading.” The instructions I was following said that once I selected the downloaded file, “Your software will install automatically.”
Once you start thinking about the middle voice in English, you’ll start to notice it everywhere.
The last two sentences show that sometimes it’s hard to say for sure that a verb is an implicit reflexive, an anticausative, or a middle-voice verb. On the one hand, “Your software will install automatically” means more or less the same thing as “Your software will install itself,” so maybe “install” is an implicit reflexive. On the other hand, it also means more or less the same thing as “Your software will install all by itself,” which makes it look more like an anticausative. And finally, if you don’t give any thought to the agent at all, and just go with the flow, the sentence just looks like another middle-voice construction. That’s probably why these RAM meanings tend to pattern together so often. There are situations where it’s just not clear whether they involve just one participant, or two. If you use the same verb forms for all these situations, context can do most of the work of resolving them into the different kinds of RAM meanings, or it can leave it conveniently ambiguous.
Alexiadou, Artemis, and Edit Doron. "The Syntactic Construction of Two Non-Active Voices: Passive and Middle." Journal of Linguistics 48.1 (2012): 1-34. Print.
Hundt, Marianne. English Mediopassive Constructions : A Cognitive, Corpus-Based Study of their Origin, Spread, and Current Status. 58 Vol. Amsterdam: Rodopi, 2007. Print.
Bradley, Ryan. "The Incredible! Shrinking! Airplane!" Popular Science (Fall 2018): 52-9. Print.
Kaufmann, Ingrid. "Middle Voice." Lingua 117.10 (2007): 1677-714. Print.