…when we say that many things are, approximately, springs? Well, as you learned (or will learn) in Calculus II, any function in the neighborhood of a point can be approximated by a Taylor series. The same is true for a force: a force is just a function, typically of coordinates. The first term of interest in a Taylor expansion is the linear term. Any system with a force linear in displacement behaves like a spring. This is why many things can be approximated by springs."