Even if the gods did exist, the Epicureans argued, they didn't care about us. Rather, everything comes from nature, and all that really exists are atoms and void, moving and congregating.

About 70% of what I've written about is centered on the clashes and conformities between the emerging life and physical sciences and older metaphysical frameworks in the 17th and 18th centuries. The other 30% consists of one-off essays or researches into other intriguing contemporary topics such as visual experience, aesthetics, social justice issues, and the epistemology of moral knowledge.

You can reasonably make the intellectual journey from thinking it's permissible to eat shrimp to thinking it's not permissible, or vice versa, whereas our slavery journey was uni-directional. We are as certain we are not going back to that old kind of slavery as we are that we aren't going back to the geocentric universe.

For the chemists, who wanted to manufacture new medicines and elixirs and transform base substances into noble ones, the notion that there was no metaphysical barrier to doing so - it was just a matter of getting the particles into new arrangements - was encouraging. That was the Baconian programme.

Epicurus was in favour of friendly sex but not of grand passions or marriage and children, viewing them as sources of trouble and vexation.

Moral theory develops from the divine command theory of medieval Christian philosophy, mixed up with a bit of ancient pagan virtue theory, to the purely secular moral sentiment and interpersonal reaction theories of Smith and Hume, to Kant's attempt to restore command theory but with something supersensible in the individual rather than God as the source of authority.

Morality has in the past made progress when we broadened the category of things we weren't permitted to harm (animals, 'infidels'); saw through some delusions and rationalisations about what harms are good for people themselves (prison punishment, hysterectomies for unhappy 1950s wives); and readjusted our for-the-good of others criteria so as to demand only reasonable sacrifices (ceasing to use children as handy chimney sweeps).