of a limited number of marks
which, for all any reader is apt to know, are purely
arbitrary." ("English Composition.")

In this paragraph every sentence is a repetition of some part of the
opening or topic sentence, and serves to explain it.

Second, by telling the obverse.

Second, _a proposition may be explained by telling what it is not._ At
times this is as valuable as telling what it is. Care should be taken
that the thing excluded or denied have some likeness to the
proposition or term being explained; that the two be really in some
danger of being confused. Unless to a hopelessly ignorant person, it
would not explain anything to say "a horse is not a man;" but to
assert that "a whale is not a fish, though they have many points in
common," would prepare the way for an explanation of what a whale is.
The obverse statement is nearly always followed by a repetition of
what the thing is.

The following from Newman illustrates the method:

"Now what is Theology? First, I will tell you what it is
not. And here, in the first place (though of course I speak
on the subject as a Catholic), observe that, strictly
speaking, I am not assuming that Catholicism is true, while
I make myself the champion of Theology. Catholicism has not
formally entered into my argument hitherto, nor shall I just
now assume any principle peculiar to it, for reasons which
will appear in the sequel, though of course I shall use
Catholic language. Neither, secondly, will I fall into the
fashion of the day, of identifying Natural Theology with
Physical Theology; which said Physical Theology is a most
jejune study, considered as a science, and really no science
at all, for it is ordinarily no more than a series of pious
or polemical remarks upon the physical world viewed
religiously, whereas the word 'Natural' comprehends man and
society, and all that is involved therein, as the great
Protestant writer, Dr. Butler, shows us. Nor, in the third
place, do I mean by Theology polemics of any kind; for
instance, what are called 'Evidences of Religion,' or 'the
Christian Evidences.'... Nor, fourthly, do I mean by
Theology that vague thing called 'Christianity,' or 'our
common Christianity,' or 'Christianity the law of the land,'
if there is any man alive who can tell what it is....
Lastly, I do not understand by Theology