Diathesis alternation

Diathesis alternation is a fancy way of talking about how different things can be done to a subject in a sentence. It's like choosing whether to eat an apple whole, cut it into slices, or make it into a pie. The subject of a sentence is the thing that the sentence is talking about, like "the cat" or "the car."

Diathesis alternation gives writers and speakers different options for how they want to talk about what's being done to the subject. One way is called the active voice, which means the subject is doing the action. For example, "The boy kicked the ball." The boy is doing the kicking, and the ball is receiving the action.

Another way is called the passive voice, which means the subject is having the action done to it. For example, "The ball was kicked by the boy." Here, the ball is the subject, and it's not doing anything. Instead, the boy is doing something to the ball.

Diathesis alternation lets us change between these two voices to express different things. For example, "The boy kicked the ball" sounds more direct and clear than "The ball was kicked by the boy," but the passive voice might be more appropriate in some situations, like when we don't know who did the kicking or when we want to put more focus on the ball than on the boy.