Now the material of enthymemes is derived from
four sources—probabilities, examples, necessary signs, and signs.
Conclusions are drawn from probabilities, when based upon things which most
commonly occur or seem to occur; from examples, when they are the result of
induction from one or more similar cases, and when one assumes the general and
then concludes the particular by an example; from necessary signs, when based
upon that which is necessary and ever1
exists; from signs, when
their material is the general or
the particular, whether
true or not. Now, the probable being not what occurs invariably but only for the
most part, it is evident that enthymemes of this character can always be refuted
by bringing an objection.