If used to express presumption in past time, shouldn't if you had be if you had had? That is, if expressing unreal past situations, the sentence should have the structure 'if S + had p.p. ~, S + would have p.p.? Why not in the passage?
The chief way in which innovation changes our lives is by enabling people to work for each other. As I have argued before, the main theme of human history is that we become steadily more specialized in what we produce, and steadily more diversified in what we consume: we move away from precarious self-sufficiency to safer mutual interdependence. By concentrating on serving other people’s needs for forty hours a week — which we call a job — you can spend the other seventy-two hours (not counting fifty-six hours in bed) drawing upon the services provided to you by other people. Innovation has made it possible to work for a fraction of a second in order to be able to afford to turn on an electric lamp for an hour, providing the quantity of light that would have required a whole day’s work if you had to make it yourself by collecting and refining sesame oil or lamb fat to burn in a simple lamp, as much of humanity did in the not so distant past.
