[jonnybgood]

I believe it comes directly from conventional math exposition. In a general form it’s about emphasis.

“The change of subject from “The dog bit the boy” to “the boy was bitten by the dog” is similar to the change of subject in a formula, as for example … In each case, the two sentences state the same relationship, but with different emphasis.” [1]

[1] https://medium.com/q-e-d/that-loser-woman-mathematician-who-...

[no_identd]

Speaking of subject, I find it helpful to have awareness of changes in agent/patient, and not just object/subject:

https://en.wikipedia.org/wiki/Thematic_relation

https://en.wikipedia.org/wiki/Agent_(grammar)

https://en.wikipedia.org/wiki/Patient_(grammar)