uppose we say that,
if he has knowledge we rejoice to hear it, but knowledge must be of
something which is, as ignorance is of something which is not; and there
is a third thing, which both is and is not, and is matter of opinion
only. Opinion and knowledge, then, having distinct objects, must also
be distinct faculties. And by faculties I mean powers unseen and
distinguishable only by the difference in their objects, as opinion
and knowledge differ, since the one is liable to err, but the other
is unerring and is the mightiest of all our faculties. If being is
the object of knowledge, and not-being of ignorance, and these are the
extremes, opinion must lie between them, and may be called darker than
the one and brighter than the other. This intermediate or contingent
matter is and is not at the same time, and partakes both of existence
and of non-existence. Now I would ask my good friend, who denies
abstract beauty and justice, and affirms a many beautiful and a
many just, whether everything he sees is not in some point of view
different--the beautiful ugly, the pious impious, the just unjust? Is
not the double also the half, and are not heavy and light relative terms
which pass into one another? Everything is and is not, as in the old
riddle--'A man and not a man shot and did not shoot a bird and not a
bird with a stone and not a stone.' The mind cannot be fixed on either
alternative; and these ambiguous, intermediate, erring, half-lighted
objects, which have a disorderly movement in the region between being
and not-being, are the proper matter of opinion, as the immutable
objects are the proper matter of knowledge. And he who grovels in the
world of sense, and has only this uncertain perception of things, is not
a philosopher, but a lover of opinion only...

The fifth book is the new beginning of the Republic, in which the
community of property and of family are first maintained, and the
transition is made to the kingdom of philosophers. For both of these
Plato, after his manner, has been preparing in some chance words of Book
IV, which fall unperceived on the reader's mind, as they are supposed
at first to have fallen on the ear of Glaucon and Adeimantus. The
'paradoxes,' as Morgenstern terms them, of this book of the Republic
will be reserved for another place; a few remarks on the style, and some
explanations of difficulties, may be briefly added.

First, there is the image of the waves, which serves for a sort o