Abbildungen der Seite
PDF
EPUB
[ocr errors]
[merged small][ocr errors][merged small][merged small]

matter.

IN the First Analytics, fyllogisms are con

fidered in respect of their form ; they are now to be considered in respect of their

The form lies in the necessary connection between the premises and the conclusion; and where such a connection is wanting, they are said to be informal, or vicious in point of form.

But where there is no fault in the form, there may

be in the matter; that is, in the propositions of which they are composed, which may be true or false, probable or improbable

When the premises are certain, and the conclusion drawn from them in due form, this is demonstration, and produces scio ence. Such fyllogisms are called apodica

tical;

3 D 2

tical; and are handled in the two books of the Last Analytics. When the premises are not certain, but probable only, such fyllogisins are called dialectical; and of them he treats in the eight books of the Topics. But there are some fyllogisms which seem to be perfect both in matter and form, when they are not really so: as, a face may seem beautiful which is but painted. These being apt to deceive, and produce a false opinion, are called fophiftical; and they are the subject of the book concerning Sophisms.

To return to the Last Analytics, which treat of demonstration and of science: We ihall not pretend to abridge these books; for Aristotle's writings do not admit of abridgement: no man in fewer words can say what he says; and he is not often guilty of repetition. We shall only give some of his capital conclusions, omitting his long reasonings and nice distinctions, of which his genius was wonderfully productive.

All demonstration must be built upon principles already known; and these upon others of the same kind; until we come at last to first principles, which neither

can

can be demonstrated, nor need to be, being evident of themselves.

We cannot demonstrate things in a circle, supporting the conclusion by the premises, and the premises by the conclufion. Nor can there be an infinite number 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 demonstration.

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

4. What

tive; the demonstration of an universal to that of a particular; and direct demonstration to that ad absurdum.

The principles are more certain than the conclusion.

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

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 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 righe 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

[ocr errors]

the manner in which we acquire first prin-
ciples, which are the foundation of all de
monstration. These are not innate, be-
cause we may be for a great part of life
ignorant of them : nor can they be dedu-
ced 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 fenfe. The senses
give us informations of individual things,
and from these by induction we draw ge-
neral conclusions : for it is a maxim with
Aristotle, That there is nothing in the un-
derstanding 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.

[ocr errors]

Sect. 2. Of the Topics.

The professed design of the Topics is, to Thew a method by which a man may be able to reason with probability and con

fistency

« ZurückWeiter »