learned is almost nothing in comparison with that of which I am ignorant,
and to the knowledge of which I do not despair of being able to attain;
for it is much the same with those who gradually discover truth in the
sciences, as with those who when growing rich find less difficulty in
making great acquisitions, than they formerly experienced when poor in
making acquisitions of much smaller amount.  Or they may be compared to the
commanders of armies, whose forces usually increase in proportion to their
victories, and who need greater prudence to keep together the residue of
their troops after a defeat than after a victory to take towns and
provinces.  For he truly engages in battle who endeavors to surmount all
the difficulties and errors which prevent him from reaching the knowledge
of truth, and he is overcome in fight who admits a false opinion touching
a matter of any generality and importance, and he requires thereafter much
more skill to recover his former position than to make great advances when
once in possession of thoroughly ascertained principles.  As for myself, if
I have succeeded in discovering any truths in the sciences (and I trust
that what is contained in this volume 1 will show that I have found some),
I can declare that they are but the consequences and results of five or
six principal difficulties which I have surmounted, and my encounters with
which I reckoned as battles in which victory declared for me.  I will not
hesitate even to avow my belief that nothing further is wanting to enable
me fully to realize my designs than to gain two or three similar
victories; and that I am not so far advanced in years but that, according
to the ordinary course of nature, I may still have sufficient leisure for
this end.  But I conceive myself the more bound to husband the time that
remains the greater my expectation of being able to employ it aright, and
I should doubtless have much to rob me of it, were I to publish the
principles of my physics:  for although they are almost all so evident that
to assent to them no more is needed than simply to understand them, and
although there is not one of them of which I do not expect to be able to
give demonstration, yet, as it is impossible that they can be in
accordance with all the diverse opinions of others, I foresee that I
should frequently be turned aside from my grand design, on occasion of the
opposition which they would be sure to awaken.

It may be said, that these oppositions would be useful both in making me
aware of my errors, and, if my speculations contain anything of value, in
bringing others to a fuller understanding of it; and still farther, as
many can see better than one, in leading others who are now beginning to
avail themselves of my principles, to assist me in turn with their
discoveries.  But though I recognize my extreme liability to error, and
scarce ever trust to the first thoughts which occur to me, yet-the
experience I have had of possible objections to my views prevents me from
anticipating any profit from them.  For I have already had frequent proof
of the judgments, as well of those I esteemed friends, as of some others
to whom I thought I was an object of indifference, and even of some whose
malignancy and envy would, I knew, determine them to endeavor to discover
what partiality concealed from the eyes of my friends.  But it has rarely
happened that anything has been objected to me which I had myself
altogether overlooked, unless it were something far removed from the
subject:  so that I have never met with a single critic of my opinions who
did not appear to me either less rigorous or less equitable than myself.
And further, I have never observed that any truth before unknown has been
brought to light by the disputations that are practised in the schools;
for while each strives for the victory, each is much more occupied in
making the best of mere verisimilitude, than in weighing the reasons on
both sides of the question; and those who have been long good advocates
are not afterwards on that account the better judges.

As for the advantage that others would derive from the communication of my
thoughts, it could not be very great; because I have not yet so far
prosecuted them as that much does not remain to be added before they can
be applied to practice.  And I think I may say without vanity, that if
there is any one who can carry them out that length, it must be myself
rather than another:  not that there may not be in the world many minds
incomparably superior to mine, but because one cannot so well seize a
thing and make it one's own, when it has been learned from another, as
when one has himself discovered it.  And so true is this of the present
subject that, though I have often explained some of my opinions to persons
of much acuteness, who, whilst I was speaking, appeared to understand them
very distinctly, yet, when they repeated them, I have observed that they
almost always changed them to such an extent that I could no longer
acknowledge them as mine.  I am glad, by the way, to take this opportunity
of requesting posterity never to believe on hearsay that anything has
proceeded from me which has not been published by myself; and I am not at
all astonished at the extravagances attributed to those ancient
philosophers whose own writings we do not possess; whose thoughts,
however, I do not on that account suppose to have been really absurd,
seeing they were among the ablest men of their times, but only that these
have been falsely represented to us.  It is observable, accordingly, that
scarcely in a single instance has any one of their disciples surpassed
them; and I am quite sure that the most devoted of the present followers
of Aristotle would think themselves happy if they had as much knowledge of
nature as he possessed, were it even under the condition that they should
never afterwards attain to higher.  In this respect they are like the ivy
which never strives to rise above the tree that sustains it, and which
frequently even returns downwards when it has reached the top; for it
seems to me that they also sink, in other words, render themselves less
wise than they would be if they gave up study, who, not contented with
knowing all that is intelligibly explained in their author, desire in
addition to find in him the solution of many difficulties of which he says
not a word, and never perhaps so much as thought.  Their fashion of
philosophizing, however, is well suited to persons whose abilities fall
below mediocrity; for the obscurity of the distinctions and principles of
which they make use enables them to speak of all things with as much
confidence as if they really knew them, and to defend all that they say on
any subject against the most subtle and skillful, without its being
possible for any one to convict them of error.  In this they seem to me to
be like a blind man, who, in order to fight on equal terms with a person
that sees, should have made him descend to the bottom of an intensely dark