On reading this thread: https://www.physicsforums.com/threads/newtons-law-of-gravitation.835627/ I started to wonder (not for the first time) when (and where?) the term "subject" became common, for the variable on the left side of an equation or formula? I'm pretty sure nobody talked about "changing the subject of an equation" when I was in school in the 1960s, or in college in the 1970s, in the US. I don't remember students in my college physics classes using it from the 1980s onwards. I've always said something like "solving the equation for <variable name>." However, I've been pretty much out of touch with trends in high school algebra-instruction. Or maybe this is a British versus US thing?