not understand it.

A third has mastered the laws of proportion mathematically,
as he has found them in Euclid or other geometrical treatise.

A fourth with the plain numbers of 1, 2, and 3,
sees for himself by simple intuitive force that 1:2 = 3:6.

Of these several kinds of knowledge the third and
fourth alone deserve to be called knowledge, the others
being no more than opinions more or less justly
founded. The last is the only real insight, although
the third, being exact in its form, may be depended
upon as a basis of certainty. Under this last, as
Spinoza allows, nothing except the very simplest truths
non nisi simplicissimae veritates can be perceived, but,
such as they are, they are the foundation of all after
science; and the true ideas, the verae ideae, which are
apprehended by this faculty of intuition, are the
primitive instruments with which nature has furnished us.
If we ask for a test by which to distinguish them, he
has none to give us. "Veritas," he says to his friends,
in answer to their question, "veritas index sui est et
falsi. Veritas se ipsam patefacit." These original
truths are of such a kind that they cannot without
absurdity even be conceived to be false; the opposites
of them are contradictions in terms:--"Ut sciam me
scire necessario debeo prius scire. Hinc pater quod
certitudo nihil est praeter ipsam essentiam objectivam.
...Cum itaque veritas nullo egeat signo, sed sufficiat
habere essentiam rerum objectivam, aut quod idem
est ideas, ut omne tollatur dubium; hint sequitur quod
vera non est methodus, signum veritatis quaerere post
acquisitionem idearum; sed quod vera methodus est
via, et ipsa vetitas, aut essentiae objectivae rerum, aut
ideae (omnia illa idem significant) debito ordine quaerantur."
(De Emend. Intell.)

The opinion of this Review on reasonings of such
a kind has been too often expressed to require us now
to say how insecure they appear to us. When we remember
the thousand conflicting opinions, the truth
of which their several advocates have as little doubted
as they have doubted their own existence, we require
some better evidence than a mere feeling of certainty;
and Aristotle's less pretending canon promises a safer
road. Ho pasi dokei, "what all men think," says Aristotle,
touto einai phamen, "this we say is,"--"and if you will not
have this to be a fair ground of conviction, you will
scarcely find one which will serve you better." We are
to see, however, wha