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can be demonstrated, nor need to be, being evident of themselves.
We cannot demonstrate things in a circle, fupporting the conclusion by the premises, and the premises by the conclufion. Nor can there be an infinite nuinber of middle terms between the first principle and the conclusion.
In all demonstration, the first principles, the conclusion, and all the intermediate propositions, must be necessary, general, and eternal truths : for of things fortuitous, contingent, or mutable, or of individual things, there is no deinonstration.
Some demonstrations prove only, that the thing is thus affected; others prove, why it is thus affected. The former may be drawn from a remote cause, or from an effect : but the latter must be drawn from an immediate cause; and are the most perfect.
The first figure is best adapted to demonstration, because it affords conclufions universally affirmative; and this figure is commonly used by the mathematicians.
The demonstration of an affirmative proposition is preferable to that of a nega
tive; the demonstration of an universal to that of a particular ; and direct demonftration to that ad absurdum.
The principles are more certain than the conclufion.
There cannot be opinion and science of the same thing at the same time.
In the second book we are taught, that the questions that may
with regard to any thing, are four: 1. Whether the thing be thus affected. 2. Why it is thus affected. 3. Whether it exists. it is.
The last of these questions Aristotle, in good Greek, calls the What is it of a thing. The schoolmen, in very barbarous Latin, called this, the quiddity of a thing. This quiddity, he proves by many arguments, cannot be demonstrated, but must be fixed by a definition. This gives occasion 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 also of the four kinds of causes ; 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 demonstration. These are not innate, because we may be for a great part of life ignorant of them : nor can they be deduced demonstratively from any antecedent knowledge, otherwise they would not be first principles. Therefore he concludes, that first principles are got by induction, from the informations of sense. The senses give us informations of individual things, and from these by induction we draw general conclusions : for it is a maxim with Aristotle, That there is nothing in the understanding which was not before in some sense.
The knowledge of first principles, as it is not acquired by demonstration, ought not to be called science; and therefore he calls it intelligence.
SECT. 2. Of the Topics.
The professed design of the Topics is, to shew a method by which a man may be able to reason with probability and con3 D 2
Every question is either about the genus of the fübject, or its specific difference, or somen thing proper to it; or something accidental.
To prove that this division is complete, Aristotle reasons thus: Whatever is attributed to a subject, it must either be, that the subject can be reciprocally attributed to it, or that it cannot. If the subject and attribute can be reciprocated, the attribute either declares what the subject is, and then it is a definition ; or it does not declare what the subject is, and then it is a
v property. If the attribute cannot be reciprocated, it must be something contained in the definition, or not. If it be contain
. ed in the definition of the subject; it must be the genus of the subject, or its specific difference; for the definition consists of these two. If it be not contained in the definition of the subject, it must be an accident.
The furniture proper to fit a man for arguing dialectically may be reduced to these four heads ; 1. Probabie propositions of all forts, which may on occasion be assumed
in an argument.
2. Distinctions of words which are nearly of the same signification. 3. Distinctions of things which are not so far asunder but that they may be taken for one and the same. 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 same, or different; and the topics for proving one thing to be better or worse than another.
In this enumeration of topics, Aristotle has fhewn more the fertility of his genius, than the accuracy of method. The writers of logic seem to be of this opinion : for I know none of them that has followed him closely upon this subject. They have considered the topics of argumentation as reducible to certain axioms. For instance, when the question is about the genus
of a thing, it must be determined by some axiom about genus and species ; when it is about a definition, it must be determined by fome axiom relating to definition, and things defined : and so of other questions.