or opinion of any writer, or inquiring into any facred doctrine of fcripture, we come to a furer determination of the truth by several diftinct places wherein the fame thing is expreffed or plainly implied; because it is not probable that an honest skilful reader fhould miftake the meaning of the writer in many places, as he may in one

or two.

(3) When we would prove the importance of any fcriptural doctrine or duty, the multitude of texts, wherein it is repeated and inculcated upon the reader, feems naturally to inftruct us that it is a matter of greater importance than other things which are but flightly or fingly mentioned in the bible.

(4.) In fearching out matters of fact in times past, or in diftant places, (in which cafe moral evidences is fufficient, and moral certainty is the utmoft which can be attained) here we derive a greater affurance of the truth of it by a number of persons, or a multitude of circumftances concurring to bear witness of it.

(5.) From many experiments in natural philofophy we more fafely infer a general theorem, than we can from one or two.

(6.) In matters which require present practice, both facred and civil, we must content ourselves oftentimes with a mere preponderation of probable reasons or arguments. Where there are feveral reafons on each fide, for and against a thing that is to be done or omitted, a small argument added to the heap may justly turn the balance on one fide, and determine the judgment, as I have noted in the fecond part of Logic.

To conclude; a growing acquaintance with matters of learning, and a daily improvement of our understandings in affairs human and divine, will beft teach us to judge and diftinguifh in what cafes the number of arguments add to their weight and force: it is only experience can fully inform us when we must be determined by probable topics, and when we must seek and expect demonstrations.

Rule VI. Prove your conclufion (as far as poffible) by fome propofitions that are in themfelves more plain, evident and certain than the conclufion; or at least fuch as are more known, and more intelligible to the perfon whom you would convince. If we neglect this rule,

we shall endeavour to enlighten that which is obfcure by fomething equally or more obfcure, and to confirm. that which is doubtful, by fomething equally or more uncertain. Common fenfe dictates to all men, that it is impoffible to establish any truth, and to convince others of it, but by fomething that is better known to them than that truth is.

1

Rule VII. Labour in all your arguings to enlighten the understanding, as well as to conquer and captivate the judgment. Argue in fuch a manner as may give a natural, diftinct, and folid knowledge of things to your hearers, as well as to force their affent by a mere proof of the question. Now to attain this end, the chief topic or medium of your demonftration fhould be fetched, as much as poflible, from the nature of the thing: to be proved, or from those things which are most naturally connected with it.

Geometricians fometimes break this rule without neceflity, two ways, (viz.)

1. When they prove one propofition only by fhewing what abfurdities will follow if the contradictory propofition be fuppofed or admitted. This is called Reductio ad abfurdum, or Demonflratio per impoffibible; as for instance, when they prove all the Radii of a circle to be equal, by fuppofing one Radius to be longer or fhorter than another, and then fhewing what abfurd confequences will follow. This, I confefs, forces the affent, but it does not enlighten the mind by fhewing the true reafon and caufe why all Radii are e-qual, which is derived from the very conftruction of a circle for fince a circle is formed by fixing one end of a ftrait line in the centre, and moving the other end. round, (or, which is all one, by compafles, kept open to a certain extent) it follows evidently that every part of the circumference being thus defcribed muft be equallydiftant from the centre, and therefore the Radii, which

*Note, This rule chiefly refers to the establishment of fome truth,, rather than to the refutation of error. It is a very common and ufe. ful way of arguing to refute a falfe propofition, by fhewing what evident falfehood or abfurdities will follow from it. For what propofition foever is really abfurd and falfe; does effectually prove that principle to be falfe from which it is derived; fo that this way of refuting an error is not fo ufually called "Reductio ad abfurdum."

are lines from the centre to the circumference, muft be all equal.

2. Geometricians forget this rule when they heap up many far fetched lines, figures and proportions to prove fome plain, fimple, and obvious propofition. This is called a Demonstration per aliena et remota, or an argument from unnatural and remote mediums: as if in order to prove the Radii of a circle are all equal, I fhould make feveral triangles and fquares about the circle, and then from fome properties and propofitions of fquares and triangles prove that the Radii of a circle are equal.

Yet it must be confeffed, that sometimes fuch queftions happen, that it is hardly poffible to prove them by direct arguments drawn from the nature of things, &c. and then it may not only be lawful, but neceffary to ufe indirect proofs, and arguments drawn from remote mediums, or from the abfurdity of the contradictory fuppofitions.

Such indirect and remote arguments may also be fometimes ufed to confirm a propofition which has been before proved by arguments'more direct and immediate.

VIII. Rule. Though arguments fhould give light to the fubject, as well as conftrain the affent, yet you muit learn to diftinguish well between an explication and an argument; and neither impofe upon yourselves, nor fuffer yourfelves to be impofed upon by others, by miftaking a mere illuftration for a convincing reafon.

Axioms themselves, or felf-evident propofitions may want an explication or illuftration, though they are not to be proved by reasoning..

Similitudes and allufions have oftentimes a very hapPY influence to explain fome difficult truth, and to render the idea of it familiar and eafy. Where the refemblance is just and accurate, the influence of a fimile may proceed fo far as to fhew the poffibility of the thing in queftion: but fimilitudes muit not be taken as a folid proof of the truth or exiftence of those things to which they have a refemblance. A too great deference paid to fimilitudes, or an utter rejection of them feem to be two extremes, and ought to be avoide ed. The late ingenious Mr Locke, even in his inquiries after truth, makes great ufe of fimilies for frequent

illustration, and is very happy in the invention of them though he warns us alfo leit we mistake them for conclufive arguments.

Yet let it be noted here, that a parable or a fimilitude used by any author, may give a fufficient proof of the true fenfe and meaning of that author, provided that we draw not this fimilitude beyond the scope and defign for which it was brought as when our Saviour affirms, Rev. iii 3. I will come to thee as a thief; this will plainly prove that he deferibes the unexpectedness of his appearance, though it will by no means be drawn to fignify any injuftice in his defign.

IX. Rule. In your whole courfe of reasoning keep your mind. Jincerely intent in the purfuit of truth; and follow folid argument wherefoever it leads you. Let not a party Ipirit, nor any paffion or prejudice whatfoever, itup or avert the current of your reafoning in queft of true knowledge.

When you are inquiring therefore into any fubject, maintain a due regard to the arguments and objections on both fides of a question: confider, compare, and balance them well before you determine for one side. It is a frequent, but a very faulty practice to hunt after arguments, only to make good one side of a queftion, and entirely to neglect and refuse those which favour the other side. If we have not given a due weight to arguments on both sides, we do but wilfully mifguide our judgment, and abufe our reafon by forbidding its fearch after truth. When we espouse opinions by a fecret biafs on the mind through the influences of fear, hope, honour, credit, intereft, or any other prejudice, and then feek arguments only to fupport thofe opinions, we have neither done our duty to God nor to ourselves; and it is a matter of mere chance if we ftumble upon truth in our ways to ease and preferment. The power of reafoning was given. us by our Maker for this very end, to purfue truth; and we abuse one of his richest gifts, if we bafely yield. up to be led aftray by any of the meaner powers of na ture, or the perishing interefts of this life. Reason itfelf, if honestly obeyed, will lead us to receive the divine revelation of the gospel, where it is duly propofed, and this will fhew us the path of life everlasting.

THE

FOURTH PART

OF

L O G I I C..

OF DISPOSITION AND METHOD..

'T is not merely a clear and distinct idea,, a wellformed proposition, or a just argument that is fufhcient to fearch out and communicate the knowledgeof a subject. There must be a variety and feries of them difpofed in a due manner, in order to attain this end and therefore it is the design of the last part of. Logic to teach us the art of method. It is that must fecure our thoughts from that confusion, darkness, and miftake which unavoidably attend the meditations and discourses even of the brightest genius who defpifes the rules of it..

1. We fhall here consider the nature of method, and: the feveral kinds of it.

2. Lay down the general rules of_method, with a few particulars under them.