In all demonftration, the firft priciples, the conclufion, and all the intermediate propofitions, must be neceffary, general, and eternal truths: for of things fortuitous, contingent, or mutable, or of individual things, there is no demonstration.

Some demonftrations prove only, that the thing is thus affected; others prove, why it is thus affected. The former may be drawn from a remote caufe, or from an effect: but the latter must be drawn from an immediate caufe; and are the most perfect,

The firft figure is beft adapted to demonstration, because it affords conclufions univerfally affirma tive; and this figure is commonly used by the mathematicians.

The demonstration of an affirmative propofition is preferable to that of a negative; the demonftration of an univerfal to that of a particular; and direct demonftration to that ad abfurdum.

The principles are more certain than the conclufion.

There cannot be opinion and science of the fame thing at the fame time.

In the second book we are taught, that the queftions that may be put with regard to any thing, are four: 1. Whether the thing be thus affected. 2. Why it is thus affected. 3. Whether it exifts. 4. What it is.

The laft of these queftions Ariftotle, in good Greek, calls the What is it of a thing. The fchool

men,

men, in very barbarous Latin, called this, the quiddity of a thing. This quiddity, he proves by many arguments, cannot be demonftrated, but must be fixed by a definition. This gives occa

fion to treat of definition, and how a right definition should be formed. As an example, he gives a definition of the number three, and defines it to be the first odd number.

In this book he treats alfo of the four kinds of caufes; efficient, material, formal, and final.

Another thing treated of in this book is, the manner in which we acquire first principles, which are the foundation of all demonftration. Thefe are not innate, because we may be for a great part of life ignorant of them: nor can they be deduced demonftratively from any antecedent knowledge, otherwise they would not be firft principles. Therefore he concludes, that firft principles are got by induction, from the informations of sense. The fenfes give us informations of individual things, and from these by induction we draw ge neral conclufions: for it is a maxim with Ariftotle, That there is nothing in the understanding which was not before in fome fenfe.

The knowledge of first principles, as it is not acquired by demonftration, ought not to be called fcience and therefore he calls it intelligence.

SECT.

SECT. 2. Of the Topics.

The profeffed defign of the Topics is, to fhew a method by which a man may be able to reafon with probability and confiftency upon every queAlion that can occur.

Every question is either about the genus of the fubject, or its specific difference, or fomething proper to it, or fomething accidental.

To prove that this divifion is complete, Ariftotle reafons thus: Whatever is attributed to a fubject, it muft either be, that the subject can be reciprocally attributed to it, or that it cannot. If the fubject and attribute can be reciprocated, the attribute either declares what the fubject is, and then it is a definition; or it does not declare what the fubject is, and then it is a property. If the attribute cannot be reciprocated, it must be fomething contained in the definition, or not. If it be contained in the definition of the fubject, it must be the genus of the fubject, or its fpecific difference; for the definition confifts of these two. If it be not contained in the definition of the fubject, it must be an accident.

The furniture proper to fit a man for arguing dialectically may be reduced to thefe four heads: 1. Probable propofitions of all forts, which may on occafion be affumed in an argument. 2. Diftinctions of words which are nearly of the fame fignification. 3. Diftinctions of things which are

not

not fo far asunder but that they may be taken for one and the fame. 4. Similitudes.

The second and the five following books are taken up in enumerating the topics or heads of argument that may be used in questions about the genus, the definition, the properties, and the accidents of a thing; and occasionally he introduces the topics for proving things to be the fame, or different; and the topics for proving one thing to be better or worse than another.

In this enumeration of topics, Aristotle has shewn more the fertility of his genius, than the accuracy of method. The writers of logic feem to be of this opinion: for I know none of them that has followed him clofely upon this fubject... They have confidered the topics of argumentation as reducible to certain axioms. For inftance, when the question is about the genus of a thing, it must be determined by fome axiom about genus and fpecies; when it is about a definition, it must be determined by fome axiom relating to definition, and things defined: and fo of other queftions. They have therefore reduced the doctrine of the topics to certain axioms or canons, and difpofed these axioms in order under certain heads.

This method feems to be more commodious and elegant than that of Ariftotle. Yet it must be acknowledged, that Aristotle has furnished the materials from which all the logicians have borrowed their doctrine of topics: and even Cicero, Quinctilian,

Quinctilian, and other rhetorical writers, have been much indebted to the Topics of Ariftotle.

He was the firft, as far as I know, who made an attempt of this kind: and in this he acted up to the magnanimity of his own genius, and that of ancient philofophy. Every fubject of human thought had been reduced to ten categories; every thing that can be attributed to any fubject, to five predicables: he attempted to reduce all the forms of reasoning to fixed rules of figure and mode, and to reduce all the topics of argumentation under certain heads; and by that means to collect as it were into one ftore all that can be faid on one fide or the other of every queftion, and to provide a grand arfenal, from which all future combatants might be furnished with arms offenfive and defenfive in every cause, fo as to leave no room to future generations to invent any thing

new.

The last book of the Topics is a code of the laws according to which à fyllogiftical difputation ought to be managed, both on the part of the affailant and defendant. From which it is evident, that this philofopher trained his difciples to contend, not for truth merely, but for victory.

SECT. 3. Of the book concerning Sophifms. A fyllogifm which leads to a falfe conclufion, muft be vicious, either in matter or form: for from true principles nothing but truth can be

juftly