What did David Hume mean by saying experimental philosophy should be applied to moral philosophy “after to natural”?

Question

In A Treatise of Human Nature by David Hume it’s written:

As the science of man is the only solid foundation for the other sciences, so the only solid foundation we can give to this science itself must be laid on experience and observation.

It is no astonishing reflection to consider, that the application of experimental philosophy to moral subjects should come after that to natural, at the distance of above a whole century; since we find in fact, that there was about the same interval betwixt the origins of these sciences; and that reckoning from THALES to SOCRATES, the space of time is nearly equal to that betwixt my Lord Bacon and some late philosophers in England, who have begun to put the science of man on a new footing, and have engaged the attention, and excited the curiosity of the public.

So true it is, that however other nations may rival us in poetry, and excel us in some other agreeable arts, the improvements in reason and philosophy can only be owing to a land of toleration and of liberty.

1. Although natural can function as a noun, that does not seem to be the case here. Is the sentence containing the bolded phrase correct? Do I read it correctly?

2. To what ”reckoning from Thales to Socrates” does Hume allude?

Answer 1

David Hume discusses how his “lord” Francis Bacon was to him pivotal in the advent of “reason” and science in his land, England, but came at the span of time of a century between him and David Hume and his contemporaries. He compared this to the distance between Ancient Greek philosophers Thales of Socrates, to indicate how foundational ideas laid by one philosopher may take a significantly long period of time to mature so that a second intellectual wave can be built atop the ideas they laid down.

David Hume claims that the “science of man” is necessarily the foundation to all other fields of knowledge; and that the “science of man” is one of empiricism, or knowledge based on the systematic observation of how the external world appears to be, as a fact - in short, a scientific attitude that claims require evidence, to be trustworthy, and their legitimacy should be sought in undertaking “experiments”.

He calls his method “experimental philosophy”, because back then, “philosophy” had a broader meaning more akin to the modern word “science” (both come from roots meaning essentially “knowing” or “knowledge”).

David Hume says that you cannot build a theory of morality without first establishing a fully adequate descriptive account of how things really are - you should not say what should be, before you have established what is (experimental science should be applied first to natural philosophy before we decide what is morally right and wrong).

This is a fundamentally atheist critique of religion, as he opposes the idea that some truths are immoral to hold, but advocates that what is “True” stands on its own, whether or not someone says it is right or wrong to believe something.

See the is/ought distinction and descriptivism vs. prescriptivism.