CHAPTER IV.

OF THE NATURE AND LAWS OF EVIDENCE.

ALL Reasoning supposes that there are certain principles in which mankind acquiesce, and which they admit as sufficient to establish, beyond all reasonable doubt, the opinions to which they yield their assent. Were this not the case, we should have no data on which to proceed in argumentation, and no criterion to which we could appeal, in any case that was doubtful to ourselves, or disputed by others. The attempt to convince another, by any process of reasoning, would, therefore, be an endless and a fruitless labour; because, whatever might be advanced in favour of any disputed point, might itself be questioned as much as the point which it was intended to establish; and thus we should go on for ever, without being able to appeal to any principle that was admitted as requiring no proof, or that was deemed sufficient to command assent, or produce conviction. We must have some ground or reason for what we believe; our opinions must be founded on something that is more evident than they are themselves; and this ground on which we rest our opinions is called Evidence. As it is necessary in all cases that we judge fairly, according to the nature of the evidence before us, we never can be good reasoners without some knowledge of the principles on which the truth of an opinion or a proposition ought to be decided on. In order, then, that Logic may be applied with propriety and effect to practical purposes, it is necessary that we be acquainted in some degree with the nature, varieties, and laws of evidence.

The methods whereby we gain an acquaintance with the different departments of knowledge are very various; and the evidence that confirms these facts has also been arranged into numerous different classes by those who have written on the subject. Buffier, Beattie, Reid, Campbell, Stewart, and many other eminent authors, have discussed the doctrine of evidence with great ability; and to their works we must refer those who wish to see this important branch of metaphysical and moral science fully discussed; a mere outline is all that can

here be attempted. These writers have differed somewhat from each other in their classification and arrangement of the sources of evidence; but in the grand principles which are laid down and developed they in a great measure agree. The simplest classification is that founded on the manner in which our assent is commanded, or our judgments formed. In some cases we immediately yield our assent to a proposition as soon as the terms in which it is expressed are understood. In other cases, our decisions are formed in consequence of a process of thought consisting of different successive steps. This method of classification arranges all evidence into two great divisions, Intuitive and Deductive-the nature and properties of which we must shortly notice.

Under Intuitive Evidence is ranked that which is derived from mathematical and physical axioms. Of this kind is the evidence attending propositions like these,-one and four make five-things equal to the same are equal to one another

-a whole is greater than its parts-a body cannot be in two places at the same time; and, in short, all axioms in arithmetic and geometry. All such propositions have an original and intrinsic evidence, which makes them, as soon as the terms in which they are couched are understood, intuitively believed. If they are not thus admitted at once, no deduction of reason, nor process of argumentation, will ever make their truth more apparent, or give them any additional evidence. All axioms of this kind are founded on some certain first principles, which we are so formed as necessarily to admit as true and undeniable, as soon as they are presented to the mind.

To this head, also, is assigned the evidence derived from the report of our senses. It is in this way we obtain our knowledge of external objects, and the conviction that they really are what they appear to be. When we see a man, or touch a table, or taste an orange, we are irresistibly led to believe that these objects exist, and that they have size, shape, colour, and the various qualities which our senses inform us they possess. We have a perfect certainty of the reality of the sensations which we experience in these instances. Our senses furnish us with evidence of the existence of everything which thus comes within the sphere of our sensations; and to

this evidence we are induced at once to give credit, without having recourse to any reasoning process to confirm its dictates. Sometimes, it is true, the apparent evidence of our senses is not correct, and not to be trusted. But in these cases the organs are not in a healthy state; or the objects are not rightly situated; or the medium is not suitable or in its proper state; hence the evidence is vitiated. But, even in these cases, we yield an assent to what our senses appear to declare; and so certain is our belief in the testimony which they give, that, unless the testimony of one sense corrected the apparent evidence of another, we should often be led astray.

The evidence of consciousness belongs also to this class. By this means we have a perfect assurance of our own existence. We know that we exist, and that we are the subjects of all that is passing in our minds. We are convinced, by evidence the most irresistible, that we think, and reason, and remember, and feel, and perform all the functions of life. The evidence derived from consciousness is so undeniable, that it has never been questioned even by the most sceptical. This evidence is absolutely essential, since without it we never should be able to carry on the common business of life; and, although the judgments thus formed cannot be moulded, as axioms are, into general positions, to which a chain of reasoning may be applied, yet they are quite as conclusive and convincing as any axiom.

Another branch of intuitive evidence arises from what has been called common sense. This is a source of knowledge common to all mankind: it is possessed in different degrees by different persons, but none are totally destitute of it, except those who are not in the possession of their faculties. It is in this way we derive our conviction of the truth of propositions like these,—whatever had a beginning had a cause -when there is contrivance and skill perceived in an effect, there must have been an intelligent cause-the course of nature will be the same to-morrow as it has been to-day; all propositions of this kind, the constitution of our mind compels us to believe, without any external proof. The evidence of common sense, being a natural dictate of the mind, is also as firmly believed as any mathematical axiom.

The evidence of memory is another branch of intuitive evidence. When events which have previously happened are recalled to the mind, we are so constituted as to give implicit confidence to what memory reports respecting them. We are convinced that the events happened, and that that which is impressed on the mind respecting them is positively certain. Remembrance, it is true, is not always accompanied with this absolute conviction since the facts which are recorded on memory are in many cases very soon partially effaced or obliterated; or, if they remain, from various causes, they may be confounded with other events, or perhaps with the mere figments of our imagination. But, if we distinctly remember any past event, we are absolutely certain that it took place, and can no more doubt respecting it, than we can doubt the testimony of our senses. It is not possible to draw the line correctly between those impressions on the memory which command instant belief, and those which are so imperfectly remembered as merely to justify supposition or opinion; nor is this at all necessary, since the mind itself will afford, in most cases, all that is needed to regulate our decisions and conduct. But, whenever the truths which are called up in the mind are clearly and distinctly recognised, we implicitly rely on the evidence which memory thus affords. And experience will materially aid us in those cases in which we are doubtful whether what appears to be the intimations of memory are really so or not.

These are the principal classes into which intuitive evidence has been divided. It includes everything the evidence of which results from the mere simple contemplation of the object, and which requires no medium to confirm its truth, but the evidence which the object itself carries along with it. The classification adopted respecting the various kinds of evidence included under this head, is not perhaps perfect, or in every case uniform; as some writers prefer one division, others another; but the distinguishing characteristics by which it may be known are these: the belief attending it is instantaneous, irresistible, and universal;—wherever there is room for comparison, or any necessity for reasoning, this evidence is wanting. If, then, in any process of argumentation, an appeal is made to the evidence thus obtained, the appeal is final. The

decisions thus formed are first principles beyond which we cannot advance; and which never can be made more evident by any additional evidence or argumentation. The various attempts which learned men have made to prove that which evidently lies beyond their power to demonstrate, have only exposed them and their efforts to ridicule. First principles are the ne-plus-ultra in reasoning. These we must admit as self-evident, without being able to assign any reason for believing them, except that we are so formed as necessarily to admit them. The man that denies them is irrational, and ought not to be argued with, but commiserated.

On the other hand, Deductive Evidence is that to which we yield our assent, because we are satisfied with the proof which has been brought forward to confirm it. This branch of evidence has been divided into two principal divisions-Demonstrative and Moral. The former rests either on axioms, that is, self-evident truths which we receive intuitively on their own naked authority, or on propositions which have already been proved. To this the name scientific has been given, because science is built on this kind of evidence. But moral evidence respects truths that are contingent, and is founded on what has been called moral axioms, or the principles we derive from consciousness, common sense, and experience. It proceeds on the presumption that those principles which guide us in life are to be depended upon. It, however, admits of degrees, and may be weakened or overthrown by contrary evidence. To this the name of probable has therefore, been given. The nature of both these kinds of evidence, their properties, and varieties, must shortly be considered.

Demonstration has for its object abstract, independent truth. The propositions with which this kind of evidence is conversant, are not limited to time or place; have no necessary dependence on any existing state of things, or matters of fact; their truth lies not in conformity to the nature of things, but in conformity to themselves, or to the hypothesis which have been formed respecting them. Hence their truth is necessary and eternal. They are not only true, but it is impossible they can be false. Every assertion opposite to truths of this kind is not only false, but absurd. Thus the assertions, the whole is greater than any of its parts-if equals be taken from