CHAPTER H. 491 must be completed in order to try its force and goodness, by add- ing the absent propositions. SECT. VII. Of the middle Terms, of common Places or Topics, and Invention of Arguments. THE next division of syllogisms is according to the middle term, which is made use of in the proof of any proposition. Now the middle term (as we have hinted before) is often called argument, because the force of the syllogism depends upon it. 'We must make a little delay here to treat briefly of the doctrine of topics, or places whence middle terms or arguments are drawn. All arts and sciences have some general subjects which be, long to them, which are called topics or common places ; because middle terms are' borrowed, and arguments derived from them for the proof of the various propositions which we have occasion to discourse of. The topics of grammar, are etymology, noun, verb, construction, signification, &c. The topics of logic are genus, species, difference, property, definition, division, &c. The topics of ontology, or metaphysics, are cause, effect, ac- tion, passion,' identity, opposition, subject, adjunct, sign, &c. The topics of morality, or ethics, are law, sin, duty, authority, freedom of will, command, threatening, reward, punishment, &c. The topics of theology, are God, Christ, faith, hope, wor- ship, salvation, &c. To these several topics there belong particular observations, axioms, canons, or rules*, which are laid down in their proper sciences ; as, Grammar bath such canons, namely, Words in a different construction obtain a different sense. Words derived from the same pritnitive may probably have some affinity in their original meaning, &c. Canons in Logic are such as these, Every part of a division singly taken must contain less than the whole. A definition must be peculiar and proper 'to the thing defined. Whatever is affirmed or denied of the genus, may be affirmed or denied of the species, &c. Metaphysical canons are such as these : Final causes belong only to intelligent agents. If a na- ttiral and necessary cause operate, the. effect will follow, &c.'and there are large catalogues of many more in each distinct science. Now it has been the custom of those who teach Logic or Rhetoric, to direct their disciples when.they want an argument, to consult the several topics which are suited to their subjects of discourse, and to rummage over the definitions, divisions, and canons that belong to each topic. This is called the invention of etn argument : and it is taught with much, solemnity in some schools. e + A canon is a proposition declaring some prof,erty of the (abject which ig sot expressed is the def nitioc or division of it,
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