Don : But isn’t the standard tripartite division physics, ethics and canon? What am I missing?
Touché. Good point. And physics is the study of nature. However, physics was a fundamental component of philosophy for everyone. From Diogenes Laertius' Lives 1:18:
Philosophy has three parts, physics, ethics, and dialectic or logic. Physics is the part concerned with the universe and all that it contains; ethics that concerned with life and all that has to do with us; while the processes of reasoning employed by both form the province of dialectic. Physics flourished down to the time of Archelaus; ethics, as we have said, started with Socrates; while dialectic goes as far back as Zeno of Elea. In ethics there have been ten schools: the Academic, the Cyrenaic, the Elian, the Megarian, the Cynic, the Eretrian, the Dialectic, the Peripatetic, the Stoic, and the Epicurean.
I firmly agree that Epicurus sees the study of nature as fundamental, but other schools would probably have said something similar. That said, Epicurus also wrote to Herodotus that:
"Hence, since such a course is of service to all who take up natural science (φυσιολογίᾳ), I, who devote to the subject my continuous energy and reap the calm enjoyment of a life like this, have prepared for you just such an epitome and manual of the doctrines as a whole