Ancient Greek philosophy was divided into three sciences: physics,
ethics, and logic. This division is perfectly suitable to the nature
of the thing; and the only improvement that can be made in it is to
add the principle on which it is based, so that we may both satisfy
ourselves of its completeness, and also be able to determine correctly
the necessary subdivisions.
All rational knowledge is either material or formal: the former
considers some object, the latter is concerned only with the form of
the understanding and of the reason itself, and with the universal
laws of thought in general without distinction of its objects.
Formal philosophy is called logic. Material philosophy, however, which has
to do with determinate objects and the laws to which they are subject,
is again twofold; for these laws are either laws of nature or of
freedom. The science of the former is physics, that of the latter,
ethics; they are also called natural philosophy and moral philosophy
respectively.
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