flicting errors, skepticism on
points the most clear, dogmatism on points the most
mysterious."[18]

The comparison may be a simile or a metaphor, as when Huxley writes,
explaining "the physical basis of life:"--

"Protoplasm, simple or nucleated, is the formal basis of all
life. It is the clay of the potter: which, bake it and paint
it as he will, remains clay, separated by artifice, and not
by nature, from the commonest brick or sun-dried clod."[19]

These, then, are the methods commonly adopted for explaining terms and
propositions. First, by the use of definitions; second, by repeating
the proposition either directly or obversely, adding something to the
thought by each repetition; third, by enumerating particulars which
form the ground for the statement; fourth, by selecting an instance
which fairly illustrates the proposition; fifth, by the use of
comparisons and analogies.

The Subject.

Some general considerations regarding the choice of a subject have
been given. A subject should lend itself to the form of discourse
employed; next, it should be a subject interesting to the readers; and
third, it should be interesting to the writer and suited to his
ability. The last condition makes it advisable to limit the subject to
a narrow field. Few persons have the ability to view a general subject
in all its relations. "Books" everybody knows something of; yet very
few are able to treat this general subject in all its ramifications. A
person writing of the general topic "books" would not only be
compelled to know what a book is, what may truly be called a book, and
what is the value of books to readers, and therefore the influence of
the different kinds of literature; he would also be driven to study
the machinery for making books, the history of printing, illustrating,
and binding books, and all the mechanical processes connected with the
manufacture of books. The subject might take quite another turn, and
be the development of fiction or drama; it might be a discussion of
the influences, political or social, that have moulded literature; it
might be a study of character as manifested in an author's works. No
one is well fitted to write on the general topic "books." A subject
should be limited.

The Subject should allow Concrete Treatment.

For young persons _the subject should be so selected and stated that
the treatment may be concrete._ As persons advance they make more
gen