The Principles of Philosophy | Page 9

the nature of the earth, and of all

the bodies that are most generally found upon it, as air, water, fire, the
loadstone and other minerals. In the next place it is necessary also to
examine singly the nature of plants, of animals, and above all of man,
in order that we may thereafter be able to discover the other sciences
that are useful to us. Thus, all Philosophy is like a tree, of which
Metaphysics is the root, Physics the trunk, and all the other sciences the
branches that grow out of this trunk, which are reduced to three
principal, namely, Medicine, Mechanics, and Ethics. By the science of
Morals, I understand the highest and most perfect which, presupposing
an entire knowledge of the other sciences, is the last degree of wisdom.
But as it is not from the roots or the trunks of trees that we gather the
fruit, but only from the extremities of their branches, so the principal
utility of philosophy depends on the separate uses of its parts, which we
can only learn last of all. But, though I am ignorant of almost all these,
the zeal I have always felt in endeavouring to be of service to the public,
was the reason why I published, some ten or twelve years ago, certain
Essays on the doctrines I thought I had acquired. The first part of these
Essays was a "Discourse on the Method of rightly conducting the
Reason, and seeking Truth in the Sciences," in which I gave a summary
of the principal rules of logic, and also of an imperfect ethic, which a
person may follow provisionally so long as he does not know any better.
The other parts were three treatises: the first of Dioptrics, the second of
Meteors, and the third of Geometry. In the Dioptrics, I designed to
show that we might proceed far enough in philosophy as to arrive, by
its means, at the knowledge of the arts that are useful to life, because
the invention of the telescope, of which I there gave an explanation, is
one of the most difficult that has ever been made. In the treatise of
Meteors, I desired to exhibit the difference that subsists between the
philosophy I cultivate and that taught in the schools, in which the same
matters are usually discussed. In fine, in the Geometry, I professed to
demonstrate that I had discovered many things that were before
unknown, and thus afford ground for believing that we may still
discover many others, with the view of thus stimulating all to the
investigation of truth. Since that period, anticipating the difficulty
which many would experience in apprehending the foundations of the
Metaphysics, I endeavoured to explain the chief points of them in a

book of Meditations, which is not in itself large, but the size of which
has been increased, and the matter greatly illustrated, by the Objections
which several very learned persons sent to me on occasion of it, and by
the Replies which I made to them. At length, after it appeared to me
that those preceding treatises had sufficiently prepared the minds of my
readers for the Principles of Philosophy, I also published it; and I have
divided this work into four parts, the first of which contains the
principles of human knowledge, and which may be called the First
Philosophy, or Metaphysics. That this part, accordingly, may be
properly understood, it will be necessary to read beforehand the book
of Meditations I wrote on the same subject. The other three parts
contain all that is most general in Physics, namely, the explication of
the first laws or principles of nature, and the way in which the heavens,
the fixed stars, the planets, comets, and generally the whole universe,
were composed; in the next place, the explication, in particular, of the
nature of this earth, the air, water, fire, the magnet, which are the
bodies we most commonly find everywhere around it, and of all the
qualities we observe in these bodies, as light, heat, gravity, and the like.
In this way, it seems to me, I have commenced the orderly explanation
of the whole of philosophy, without omitting any of the matters that
ought to precede the last which I discussed. But to bring this
undertaking to its conclusion, I ought hereafter to explain, in the same
manner, the nature of the other more particular bodies that are on the
earth, namely, minerals, plants, animals, and especially man; finally, to
treat thereafter with accuracy of Medicine, Ethics, and Mechanics. I
should require to do this in order to give to the world a complete body
of philosophy; and I do not yet feel myself so old,- -I do not so much
distrust my strength, nor do I find myself