Full Idea
Philosophy is exploration of the rational.
Gist of Idea
Philosophy is exploration of the rational
Source
Georg W.F.Hegel (Elements of the Philosophy of Right [1821], Pref)
Book Reference
Hegel,Georg W.F.: 'Elements of the Philosophy of Right', ed/tr. Wood,Allen W. [CUP 1991], p.20
A Reaction
The only problem is that Hegel (like the Stoics) thought that nature is rational all the way down, so philosophy becomes the study of everything.