The Principles of Philosophy | Page 6

means, qualities which raised their
authority very high, so much so that those who succeeded them were
willing rather to acquiesce in their opinions, than to seek better for
themselves. The chief question among their disciples, however, was as
to whether we ought to doubt of all things or hold some as certain,--a
dispute which led them on both sides into extravagant errors; for a part
of those who were for doubt, extended it even to the actions of life, to
the neglect of the most ordinary rules required for its conduct; those, on
the other hand, who maintained the doctrine of certainty, supposing that
it must depend upon the senses, trusted entirely to them. To such an
extent was this carried by Epicurus, that it is said he ventured to affirm,
contrary to all the reasonings of the astronomers, that the sun is no
larger than it appears.
It is a fault we may remark in most disputes, that, as truth is the mean
between the two opinions that are upheld, each disputant departs from

it in proportion to the degree in which he possesses the spirit of
contradiction. But the error of those who leant too much to the side of
doubt, was not followed for any length of time, and that of the opposite
party has been to some extent corrected by the doctrine that the senses
are deceitful in many instances. Nevertheless, I do not know that this
error was wholly removed by showing that certitude is not in the senses,
but in the understanding alone when it has clear perceptions; and that
while we only possess the knowledge which is acquired in the first four
grades of wisdom, we ought not to doubt of the things that appear to be
true in what regards the conduct of life, nor esteem them as so certain
that we cannot change our opinions regarding them, even though
constrained by the evidence of reason.
From ignorance of this truth, or, if there was any one to whom it was
known, from neglect of it, the majority of those who in these later ages
aspired to be philosophers, blindly followed Aristotle, so that they
frequently corrupted the sense of his writings, and attributed to him
various opinions which he would not recognise as his own were he now
to return to the world; and those who did not follow him, among whom
are to be found many of the greatest minds, did yet not escape being
imbued with his opinions in their youth, as these form the staple of
instruction in the schools; and thus their minds were so preoccupied
that they could not rise to the knowledge of true principles. And though
I hold all the philosophers in esteem, and am unwilling to incur odium
by my censure, I can adduce a proof of my assertion, which I do not
think any of them will gainsay, which is, that they all laid down as a
principle what they did not perfectly know. For example, I know none
of them who did not suppose that there was gravity in terrestrial bodies;
but although experience shows us very clearly that bodies we call
heavy descend towards the center of the earth, we do not, therefore,
know the nature of gravity, that is, the cause or principle in virtue of
which bodies descend, and we must derive our knowledge of it from
some other source. The same may be said of a vacuum and atoms, of
heat and cold, of dryness and humidity, and of salt, sulphur, and
mercury, and the other things of this sort which some have adopted as
their principles. But no conclusion deduced from a principle which is
not clear can be evident, even although the deduction be formally valid;

and hence it follows that no reasonings based on such principles could
lead them to the certain knowledge of any one thing, nor consequently
advance them one step in the search after wisdom. And if they did
discover any truth, this was due to one or other of the four means above
mentioned. Notwithstanding this, I am in no degree desirous to lessen
the honour which each of them can justly claim; I am only constrained
to say, for the consolation of those who have not given their attention to
study, that just as in travelling, when we turn our back upon the place
to which we were going, we recede the farther from it in proportion as
we proceed in the new direction for a greater length of time and with
greater speed, so that, though we may be afterwards brought back to the
right way, we cannot nevertheless arrive at the destined place as soon
as if we had not moved backwards at all; so in philosophy, when