A false proposition joins those ideas or terms whose objects disagree, or it disjoins those whose objects agree; as, birds have no wings, brutes are immortal.

Note, it is impossible that the same proposition should be both true and false at the same time, in the same sense and in the same respect, because a proposition is but the representation of the agreement or disagreement of things; now it is impossible that the same thing should be and not be, or that the same thing should agree and not agree at the same time and in the same respect. This is a first principle of human knowledge.

Yet some propositions may seem to contradict one another, though they may be both true, but in different senses, or respects, or times; as, man was immortal in Paradise, and man was mortal in Paradise. But these two propositions must be referred to different times; as, man before his fall was immortal, but at the fall he became mortal. So we may say now, man is mortal, or man is immortal, if we take these propositions in different respects; as man is an immortal creature as to his soul, but mortal as to his body. A great variety of difficulties and seeming contradictions, both in holy scripture and other writings may be solved and explained in this manner.

The most important question on this subject is this, what is the criterion or distinguishing mark of truth? how shall we know when a proposition is really true or false? there are so many disguises of truth in the world, so many false appearances of truth, that some sects have declared there is no possibility of distinguishing truth from falsehood; and therefore they have abandoned all pretences to knowledge, and maintained strenuously that nothing, is to be known.

The first men of this humour made themselves famous in Greece by the name of Sceptics; that is, Seekers they were also called Academics, borrowing their name from academia, their school or place of study. They taught that all things are uncertain, though they allowed that some are more probable than others. After these arose the sect of Pyrrhonics,

named from Pyhrro, their master, who would not allow any proposition to be more probable than another; but professed that all things were equally uncertain. Now all these men (as an ingenious author expresses it) were rather to be called a sect of liars than philosophers, and that censure is just for two reasons-1. Because they determined concerning every proposition that it was uncertain, and believed that as a certain truth, while they professed there was nothing certain, and that nothing could be determined concerning truth or falsehood; their very doctrine gave itself the lie. 2. Because they judged and acted as other men did in the common affairs of life: they would neither run into fire nor water, though they professed ignorance and uncertainty whether the one would burn or the other drown them.

There have been some in all ages who have too much affected this humour, who dispute against every thing, under pretence that truth has no certain mark to distinguish it. Let us, therefore, enquire what is the general criterion of truth; and in order to this, it is proper to consider what is the reason why we assent to those propositions, which contain the most certain and indubitable truths, such as these, the whole is greater than a part; two and three make five.

The only reason why we believe these propositions to be true is, because the ideas of the subject and predicate appear with so much clearness and strength of evidence to agree to each other, that the mind cannot help discerning the agreement, and cannot doubt of the truth of them, but is constrained to judge them true. So when we compare the ideas of a circle and a triangle, or the ideas of an oyster and a butterfly, we see such an evident disagreement between them, that we are sure that the butterfly is not an oyster; nor is a triangle a circle. There is nothing but the evidence of the agreement or disagreement between two ideas, that makes us affirm or deny the one or the other.

Now it will follow from thence that a clear and distinct perception or full evidence of the agreement and disagreement of our ideas to one another or to things,

is a certain criterion of truth; for since our minds are of such a make, that where the evidence is exceeding plain and strong, we cannot withhold our assent; we should then be necessarily exposed to believe falsehood, if complete evidence should be found in any propositions that are not true. But surely the God of perfect wisdom, truth, and goodness would never oblige his creatures to be thus deceived; and therefore he would never have constituted us of such a frame as would render it naturally impossible to guard against error.

Another consequence is naturally derived from the former; and that is, that the only reason why we fall into a mistake is, because we are impatient to form a judgment of things before we have a clear and evident perception of their agreement or disagreement; and if we will make haste to judge while our ideas are obscure and confused, or before we see whether they agree or disagree, we shall plunge ourselves into perpetual errors. See more on this subject in an essay on the freedom of will in God and man; published 1732. Sect. i. p. 13.

Note, What is here asserted concerning the necessity of clear and distinct ideas refer chiefly to propositions, which we form ourselves by our own powers: as for propositions which we derive from the testimony of others, they will be accounted for in chap. IV.

SECT. VIII. Of certain and dubious Propositions, of Knowledge and Opinion.

Since we have found that evidence is the great criterion and the sure mark of truth; this leads us directly to consider propositions according to their evidence; and here we must take notice both of the different degrees of evidence, and the different kinds of it. Propositions according to their different degrees of evidence, are distinguished into certain and dubious*.

It may be objected, that this certainty and uncertainty being only in the mind, the division belongs to propositions rather according to the degrees of our assent, than the degrees of evidence. But it may well be answered, that the evidence here intended is that which appears so to the mind, and not the mere

Where the evidence of the agreement or disagreement of the ideas is so strong and plain, that we cannot forbid or delay our assent, the proposition is called certain; as, every circle hath a centre; the world did not create itself. An assent to such propositions is honoured with the name of knowledge.

But when there is any obscurity upon the agreement or disagreement of the ideas, so that the mind does not clearly perceive it, and is not compelled to assent or dissent, then the proposition, in a proper and phi. losophical sense, is called doubtful or uncertain; as, the planets are inhabited; the souls of brutes are mere matter; the world will not stand a thousand years louger; Dido built the city of Carthage, &c. Such uncertain propositions are called opinions.

When we consider ourselves as philosophers or searchers of truth, it would be well if we always suspended a full judgment or determination about any thing, and made further enquiries, where this plain and perfect evidence is wanting; but we are so prone of ourselves to judge without full evidence, and in some cases the necessity of action in the affairs of life constrains us to judge and determine upon a tolerable degree of evidence, that we vulgarly call those propositions certain, where we have but very little room or reason to doubt of them, though the evidence be not complete or resistless.

Certainty, according to the schools, is distinguished into objective and subjective. Objective certainty is when the proposition is certainly true in itself; and subjective, when we are certain of the truth of it. The one is in things, the other is in our minds.

But let it be observed here, that every proposition in itself is certainly true, or certainly false, For tho' doubtfulness or uncertainty seems to be a medium between certain truth and certain falsehood in our minds, yet there is no such medium in things themselves, no,

evidence in the nature of things; besides (as we shall shew im mediately) the degree of assent ought to be exactly proportiona ble to the degree of evidence; and therefore the difference is is not great, whether proportions be called certain or uncertain, according to the measure of evidence or of assent. »

not even in future events: for now at this time it is certain in itself, that Midsummer-day seven years hence will be serene, or it is certain it will be cloudy, though we are uncertain and utterly ignorant what sort of day it will be; this certainty of distant futurities is known to God only.

Uncertain or dubious propositions, i. e. opinions, are distinguished into probable or improbable.

When the evidence of any proposition is greater than the evidence of the contrary, then it is a probable opinion: where the evidence and arguments are stronger on the contrary side, we call it improbable. But while the arguments on either side seem to be equally strong, and the evidence for and against any proposition appears equal to the mind, then in common language we call it a doubtful matter. We also call it a dubious or doubtful proposition, when there is no argument on either side, as next Christmas-day will be a very sharp frost. And in general all these propositions are doubtful wherein we can percieve no sufficient marks or evidence of truth or falsehood. In such a case, the mind which is searching for truth ought to remain in a state of doubt or suspence, until superior evidence on one side or the other incline the balance of the judgment and determine the probability or certainty to the one side.

A great many propositions which we generally believe or disbelieve in human affairs, or in the sciences, have very various degrees of evidence, which yet arise not to complete certainty, either of truth or falsehood Thus it comes to pass that there are such various and almost infinite degrees of probability and improbability. To a weak probability we should give a weak assent; and a stronger assent is due where the evidence is greater, and the matter more probable. If we proportion our assent in all things to the degrees of evidence, we do the utmost that human nature is capable of in a rational way to secure itself from

error.