The moves to contractualism and utilitarianism required some extra ingredients besides mortalism, the denial that God is in charge of the world, and the doctrine that physical and psychological pain are the greatest evils.

We call 'Slavery is wrong' a moral truth because there is a specific history of theoretical investigation of a particular kind of slavery. We discussed it for centuries in metaphysical, economic, biological, and philosophical terms; we listened to all the arguments pro and con, we read all the testimonies of slaves and witnesses, and we decided. Though this 'we" is not everybody on earth, or even most people, who've never thought about slavery much.

Even if you just want to make a simple clothing item for yourself or go for a long hike in the forest - something we imagine requires absolutely no resources - you have to go to the store and buy a lot of stuff, and probably use a car.

We are now returning to the 18th century empirical approach with the new interest in the evolutionary basis of ethics, with 'experimental' moral philosophy and moral psychology. As a result, we understand better why moral formulas are experienced as ineluctable commands, even if there is no commander and even if the notion of an inescapable obligation is just superstition. So moral philosophy has made huge progress.

There's Hobbes, who understood in the 1640s that the sovereign is not an appointee of God, or even a figure of superior virtue and wisdom, but just a functional device whose role is to keep people from hurting and killing each other.

Oddly, since by now I've written quite a lot on early modern philosophers, I didn't care for the history of philosophy, which I thought dull and obscure, until I got a minor job writing articles for a children's encyclopedia in the history of science and began to make connections between science and philosophy.

For seventeenth-century astronomers, the Epicurean doctrine of multiple worlds separated by void space was seen to fit with the new Copernican system in which every star was a sun, and the universe was a vast place with no centre.