Very basic math q! See screenshot: we teach that the y-axis is at x=0, but in Fig. 4.2b, what I'd call "the y-axis" (the vertical line labeled "Response") is at x = -2. So like... what do we call that line at x = -2? Is the line at x=0 the true y-axis, and the one at x = -2 just a cosmetic one?

Both axes are essentially cosmetic?

I'd never reflected on this before, but I guess there's a convention to put the vertical edge of a graph -- which I'd call "the y-axis" but I guess technically isn't always, under the definition where "the y-axis is where x=0" -- at the minimum x value of the plotted data.