Perturbation theories is just an extension

Can you please explain "extension" in such context?

So, what worries me is, had Newton not stopped and ceded his brilliance to God, he could easily come up with prohibition theory, even invented calculus practically on a dare, perturbation theories is just an extension of calculus! Perturbation! It's a nice elegant extension, but you know Newton could have knocked this out in an afternoon, you know this. Okay.