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an Alliance with Ignorance and Impurity, as 'twas the Business of Logick to clear and refine. Alcinous, a very accurate Expositor of Plato's Logick, tells us, that this Philosopher made use of Division, Definition and Induction, as Steps by which to arrive at the first and original Source of Truth, whence his Principles are drawn, as the sure Method to think and speak wisely of all

Things; and that this was the way that he usually Carpen pra&ised. Division was a Step whereby to ascend ter in Al- from sensible Things to Intellectual: Definition ciaoum.

was a Passage from Things demonstrated, to Things undemonstrated : Introduction was a Means of discovering Truth by presuppos’d Principles. Thus by Division he proceeded to Definition; by Definition to Introduction; by Introduction to Demonstration. And Diogenes assures us, that

Plato's most common Way of Demonstrating, Cic. in was by Induction. Cicero and Quintilian agree Top. in the same Report. Yet it is to be confess’d, that Quint. 1. Socrates, in his Manner of reasoning, appliV. c. 11. ed himself more to Questions than Answers; Inductione

because the Character of his Genius was fitplurimum sufus eft ter to raise Doubts than to resolve them. Socrates. On the whole, it appears from these Prinibid.

cipies of Logick, advanced by Socrates and fioxibus Plato, that affirming all Truth to be feated in Socraticis Ideas, they with their whole School, in effect, cavendum professed themselves to know nothing ; because ne ini autė there is no Judgment to be made of singular and responde aso individual Things, but by the Senses, which they ibid.

own'd to be fallacious. And therefore Plato's ita difpu. Followers, made it their great logical Rule, tar ui ni- to embrace nothing with too easie a Belief, and hil affar to preserve the entire Liberty of their Judgment, mnes ipfe, amidit the Uncertainties which occur’d upon refellat elios. Cic. Qu. Acad. Obfflere vifis, & affenfusque fuos firmè fuftinere. Id. ibid,

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almost all Subjects. Upon this leading Maxim, 'Axatáof the general Incomprehensibility of Things, amfes. was grounded the Reformation of the Academy, uuder Lacides and Arcesilas; as also the Rise of the Pyrrhonian Sect, who doubted of the most infallible Truths. The Academicks comprehended thus much, that Things were really incomprehensible: but even this was above the Comprehension of the Pyrrhonians. This was the Logick of Plato, and this its Effect, in the Conduct of human Understanding.

IV. We meet with nothing fix'd and regular in Logick, before Aristotle. This mighty Genius, Ariftoteles so replenish'd with Understanding and Reason, utriusque obtain'd a perfect Knowledge of the Mind of partis diMan; survey'd all its Springs, and nicely distin- ale&ticæ guish'd its various Operations. No Man had"Cic. Top ever yet sounded that vast Abyss of human Thought, to make a Judgment of its Depth. Aristotle was the first that discover'd this new Way of arriving at Science by the Evidence of Demonstration, and of proceeding to such Demonstration, in a geometrical Method, by the infallible Rule of Syllogism; the most accomplish'd Work, and the greatest Effort of Spirit, that Man is capable of exerting. This is the Sum of Aristotle's Logick, the Method of which is so firm and constant, that'tis by it alone, we can attain to any absolute Certainty, in our Reasonings; as being the just Rule of all our Operations, and the true Art of Thinking. But by what Way did he arrive at this Art; or what measures did he put in practice, thus to fix the Mind of. Man, which is naturally light, and upon the Wing, and to render it unshaken in its Judgment ? It was necessary for him, at his Entrance upon this great Work to take away Еe

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all Manner of Ambiguity in Expression, to turn the incomplete Reasonings of Human Understanding into a perfect Demonstration, and yet to build this upon so unstable a Bottom as the Weakness of Word and Thought; and to be. Itow the Strength and Sted fastness of Science upon the most wandring and uncertain Subject that can be conceiy'd. In the Pursuit of this Design, he was to March through ways hitherto untraced and inaccesible; he was to divest our Thought, of all the various Dresles and changing Colours that our Expressions could give it, and to dissipate all the Clouds that the Imagination could spread before the Understanding. 'Tis with this View, that in his Book of Interpretation, which is a Kind of a Grammatica Rationis, he examines the Powers and Signification of Words; that in his Catego. ries, he states the true Notion of Terms, and by reducing them to their natural Sense, prepares them for the Uses of Definition and Divi. fion; that in his Analyticks he establishes the Rules for the Modal Conversion of all sorts of

Propositions, and for the different Figures of SylDi&um de logism, the chief Foundations of which he omni, 8 lays in three of his logical Maxims: and this dittum de

whole Frame and Construction is purely new mulio.

and his own work. In his Book of Interpretation, funt ea- he settles the Rule of contradictory Propofitidem uni

ons: His Categories are so many Dispositions and tertio,

Steps toward Demonstration: In his Books of funt eadem inter Analyticks; his Remarks are so many Demonfe. strations, and his Demonstrations so many PrinContradi- ciples. His Topicks are the Heads or common Storia ft Places of dialectical, or probable Arguments. mulere Hon pro

His Elenchi contain the Ground and Origin of all imaginable Sophisms. The two Rules he lays down for the perfect Composition of Syllogism,

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are, that there must be nothing false in the Mat- Ariftotele ter, and nothing vitious in the Form. His nemo ner

vofor in Stile is wholly free from those Languors which

fcribendo. we sometimes meet with in Plato, and from the Cic. in loose and diffus'd Manner of the Age; but is Brut. close, vigorous and concise. In a word, his purely geometrical Method of Demonstrating has ever been look'd on as fo accomplish'd, that it has been follow'd by all learned Men in all Sciences, as the most just and solid, and the most agreeable to the natural Course of Reason. And his. Construction of Syllogism, which is peculiarly Aristotle's Logick, is so complete in its kind, that it can admit of no Addition or Diminution, but for the worse. He that is happy in a sound Sense and right Judgment, can bear no other Manners, nor any other Principles of Reasoning, but those of Aristotle. And because the World being governed by Opinion, commonly disputes against Reason; the most knowing and intelligent Ages, have chiefly distinguish'd themselves from others, by the Veneration they have had for this Logick. For, to say the Truth, what he has perform'd in order to the fixing and rectifying of Reason, by cutting off all Equivocation in Terms, and Confusion in Thought, is one of the greatest Master-pieces of human Wit. Yet, it must be confess'd, that the chief Aim and Scope of this Logick, is not so much to teach Men the Art of true Reasoning, which they naturally know, as to give them Rules for the Tryal and Scrutiny of false Reasonings, and for the Guarding against the Sophisms of Zeno and Parmenides. For in Aristotle's Time, the Sophists had set up and brought into Vogue, a false Method of Reasoning, which he applies himself to detect and defeat, This is the great Idea, upon which the whole

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Design of his Logick turns, and all his Wif-
dom in giving Laws to an Art, which is to give
Laws to all besides.

V.
The Exercise of Logick was prosecuted with
dialectici so much Vigour in Zeno's School, that the Stoicks
ftoicis in refined more upon it than all the other Seats
venta, of Philosophers. Perhaps the Difficulty which
Cic. de they found in maintaining their wild and visionary
Fin,

Morals obliged them to make up in Subtilty of
Speech, what they wanted in Solidity of Do-

&trine. And therefore, to the Artifice of Zeno Cbryfippus

Eleates, the Chicane of Euclid of Megara, and ut ad in. ventionem the wise Address of Socrates, they added all the Sufficeres, Stratagem of Cleanthes and Chrysippus, both celeHelleboró brated Logicians, to compleat their new Syanimum ftem. It was to this, as Tully observes, that Perror: they applied the whole Bent of their mind and Stoicorum Study; to support their false Philosophy by an in diale- artificial Reason, while defective in that which dicis cura is true and natural. They seem to have arm'd omnis con. themselves with all the Thorns and Briars of fumitur. Cic. deci. Logick, to fence off their Adversaries; and to Orat.

have commenc'd the most formidable WrangStoicorum lers of the Schools, only to uphold the rain and ignoras

extravagant Boasts of their precarious Wisdom. dile like They made no material Change in the Logick Spinofum

of Aristotle ; but only inforced the Art of Syllodicendi gism, (which was so familiar to them) with a genus. Cic more vehement Air, with short, and lively, and de Fin. pressing Interrogations, which added a conside

rable Strength to their Method of Argument.
The tricking Humour, which so generally pre-
vail'd in their Şect, inclind them to sharpen all
their Logičk into the Cayils of Dispute ; and,
an order to this, to invent new Modes of Syllo-
gism, less natural than those of Aristotle, but
piore cunning and captious. They pretend thaç

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