XXI.  Having thus explained all the topics serviceable for arguing, the first thing to be understood is, that there is no discussion whatever to which some topic or other is not applicable; and on the other hand, that it is not every topic which is applicable to every discussion; but that different topics are suited to different subjects.

There are two kinds of inquiry:  one, infinite; the other, definite.  The definite one is that which the Greeks call [Greek:  hupothesis], and we, a cause; the infinite one, that which they call [Greek:  thesis], and which we may properly term a proposition.

A cause is determined by certain persons, places, times, actions, and things, either all or most of them; but a proposition is declared in some one of those things, or in several of them, and those not the most important:  therefore, a proposition is a part of a cause.  But the whole inquiry is about some particular one of those things in which causes are contained; whether it be one, or many, or sometimes all.  But of inquiries, concerning whatever thing they are, there two kinds; one theoretical, the other practical.  Theoretical inquiries are those of which the proposed aim is science; as, ’If it is inquired whether right proceeds from nature, or from some covenant, as it were, and bargain between men.  But the following are instances of practical inquiry:  “Whether it is the part of a wise man to meddle with statesmanship.”  The inquiries into theoretical matters are threefold; as what is inquired is, whether a thing exists, or what it is, or what its character is.  The first of these queries is explained by conjecture; the second, by definition; the third, by distinctions of right and wrong.

The method of conjecture is distributed into four parts; one of which is, when the inquiry is whether something exists; a second, when the question is, whence it has originated; a third, when one seeks to know what cause produced it; the fourth is that in which the alterations to which the subject is liable are examined:  “Whether it exists or not; whether there is anything honourable, anything intrinsically and really just; or whether these things only exist in opinion.”  But the inquiry whence it has originated, is when an inquiry is such as this, “Whether virtue is implanted by nature, or whether it can be engendered by instruction.”  But the efficient cause is like this, as when an inquiry is, “By what means eloquence is produced.”  Concerning the alterations of anything, in this manner:  “Whether eloquence can by any alteration be converted into a want of eloquence.”

XXII.  But when the question is what a thing is; the notion is to be explained, and the property, and the division, and the partition.  For these things are all attributed to definition.  Description also is added, which the Greeks call [Greek:  charaktaer].  A notion is inquired into in this way:  “Whether that is just which is useful to that person who is the more powerful.”