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