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competent authority on a doubtful question, either of speculation or practice, it is necessary, as in the case of a witness to a fact, to go through a certain process of investigation and reasoning. With regard to a witness, we must satisfy ourselves that the alleged fact occurred within the range of his senses; that he took note of it; that he apprehended properly what he observed; and that he reported it faithfully. With regard to an authority in a matter of opinion, we must be assured that he had time to study and consider the subject; that he availed himself of his opportunity; that he understood what he studied; and that he judged correctly. The process of investigating a person's competence as a guide in matters of opinion is, however, less difficult and tedious than an examination of the subject itself. For example, it would be much easier to ascertain who is a competent authority upon a question of mechanics or astronomy, than to master mechanical or astronomical science. Moreover, in practical questions, experience, which implies time, is indispensable. Thus, if any unprofessional person wished to form an independent judgment upon a medical or surgical case, with a view to its treatment, he would be unable to decide and act with safety, however powerful and cultivated his understanding might be, and whatever diligence he might be willing to use in the study of the disease. The process of determining who is a competent authority is likewise, though a process of reasoning, not appropriate to the question. The truth of the opinion rests on evidence, which would be equally conclusive if the person whose authority is adopted had never existed. It is a second-best indication of the truth; but nevertheless, in a vast number of cases, the only guide which is practicable.

§ 11. Whenever, therefore, we seek to determine who is a competent authority to guide our opinion on any subject, we should select a person who combines the qualifications which have been just enumerated. We should look out for a man able, honest, and well-versed in the subject. Some further indications of trustworthy authority, derived from other considerations, may however be obtained, which will assist us in this search.

With respect to subjects of speculation and science, the existence of an agreement of the persons having the above qualifications is the most important matter. If all the able and honest men who have diligently studied the subject, or most of them, concur, and if this consent extends over several successive

generations, at an enlightened period, and in all or most civilised countries,' then the authority is at its greatest height.

The agreement of competent judges upon a speculative opinion is analogous to the agreement of credible witnesses in their testimony to a fact. If ten credible witnesses agree in their testimony to a fact, the value of their concurrent testimony is more than ten times the value of the testimony of each. So the joint probability of the agreement of ten competent judges in a right opinion is far greater than the sum of the probabilities of the rectitude of the opinion of each taken separately. On the other hand, the joint probability of their agreement in error is far less than the sum of the probabilities of the erroneousness of the opinion of each taken separately. Supposing that each person carefully checks and verifies the process of investigation, it is highly improbable that every one, of a considerable number, should overlook an ungrounded assumption, or a flaw in the reasoning, which may have escaped the attention of the original investigator; it is also very improbable that a tendency to error, which one person may have contracted, from peculiar habits of thought, or defective means of observation, should be shared by many others. Therefore, as the agreement in a scientific opinion among competent judges widens its area, the chances of rectitude increase, and the chances of error diminish, in a perpetually accelerated ratio.3

Astronomy furnishes an example of a science, as to which there has been a general agreement of its professors for more than a century. Additional discoveries have been made during that period, and subordinate differences have been removed; but, as to the foundations of the science, there has, during that time, been a general agreement, and now even in details. This agreement extends to all scientific astronomers in all civilised countries. The astronomers of Berlin, Vienna, Milan, Paris, London, and New York, are agreed as to the motions of the bodies composing the solar system, and their mutual relations in space. The astronomical almanacs, calculated in different places, proceed on the

With respect to the influence of the political divisions of independent states in preventing the adoption of opinions without due examination, see Hume, Essay XIV.; Works, vol. iii. p. 134.

2 See Whately's Rhetoric, Part I. c. ii. § 4.

In the unanimous or general consent of numerous and impartial inquirers,' Mr. Austin finds that mark of trustworthiness which justifies reliance on authority, wherever we are debarred from the opportunity of examining the evidence for ourselves.'-Prov. of Jurisprudence Determined, p. 84.

same principles, and coincide in their predictions. These predictions, moreover, are always confirmed by the events.1

On the other hand, the dissensions of scientific writers,--of acute and disinterested men who have applied their minds with earnestness and patience to the cultivation of any science-show that this science is still in an imperfect and unsettled state, and diminish the value of the authority of all parties.

Such was the case with a large part both of the ethical and physical sciences among the ancients. The divisions of the philosophical sects into Academic, Stoic, Epicurean, &c., the peculiar tenets which each sect adopted, upon the fundamental principles of moral and natural science, the pertinacity with which these peculiarities were maintained, and the length of time during which they were transmitted in schools by a succession of teachers and disciples, weakened the authority of each, and rendered it difficult for an inquirer to give a preference to any, without learning and comparing the opinions of all."

At present, there is a prevailing approach to agreement in the sciences founded on an observation of outward nature. When controversies arise in these sciences, they are generally confined to limited questions, and to points upon which attention has been recently turned; and after a time they are settled by investigation and reasoning. In the moral and political sciences, there is a less general consensus than in the physical. Thus the science of political economy-a science which for nearly a century has been cultivated by various writers of great ability-is still (particularly with reference to certain branches of it) in a controverted and unsettled state; and, hence, the writers on political economy who have arrived at true conclusions do not carry the authority which is due to them, because those conclusions are still disputed by other scientific writers.

For this difference between the moral and political sciences on the one hand, and the physical sciences on the other, there

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1 Upon the present agreement of astronomical predictions with observation, see Whewell, Hist. of the Ind. Sciences, B. VII. c. vi. § 6.

2 See Lucian's dialogue of Hermotimus, a summary of which is appended as a note to Chapter IV. Compare what Cicero says of the sceptical method of the New Academy.-Acad. Prior. II. 3.

The reasons why authority in the moral and political sciences is less trustworthy than authority in the physical sciences, are ably set forth by Mr. Austin, Province of Jurisprudence Determined, pp. 63-67. Compare Mill, System of Logic, B. VI. c. i.

• The ancients differed and doubted more as to physics than ethics. Ut enim

are many reasons, which do not belong to this inquiry; but there is one, which, as it concerns the formation of a body of authority on the subject, may be here noticed. The physical sciences (with the partial exception of medicine) are cultivated exclusively by scientific persons, who pursue the subject merely in the interests of truth and for purposes of discovery, or expound it systematically for purposes of education. They either seek to enlarge science by new observations and inferences, or they digest existing knowledge into text-books for learners. Such, for example, is the case with mechanics, optics, geology, mineralogy, chemistry, anatomy, natural history. The treatment of these subjects is therefore always scientific. Even when the exposition is rendered popular, in order to extend the circle of learners, yet it is always based on scientific principles.

Now the moral and political sciences are, it is true, treated in a scientific manner by speculative writers. The principles of these sciences, however, are involved in the practical questions, to which the daily business of life gives birth, and which are discussed in newspapers and pamphlets, at public meetings and in large legislative assemblies. The best-ascertained principles are therefore constantly liable to be disputed, misinterpreted, or misapplied, by persons imperfectly acquainted with the subject, who take it up hastily and with a special object, and who are acted on by gusts of popular passion, or by the interests of particular individuals or classes. In this manner, opinions on moral or political subjects are multiplied, the authority of sound and scientific principles is weakened, the judgment of the public is distracted and perplexed, the difficulty of a selection of safe guides is increased, and an anarchical state of public opinion is created. On the other hand, it ought not to be overlooked that municipal or positive law, among the political sciences, receives an exclusively scientific and professional treatment; and hence the utility of institutions which promote an enlightened spirit among the leaders of the legal profession, and the importance of improvements in jurisprudence, as directing the moral sentiments of a nation.

The inconvenience of a popular treatment of the moral sciences, proceeding concurrently and in a parallel line with their scientific treatment, is illustrated by Dr. Whewell's remarks upon those

modo dixi, (says the academic interlocutor in Cicero's dialogue De Naturâ Deorum,) omnibus fere in rebus, et maxime in physicis, quid non sit citius, quam quid sit, dixerim.' I. 21. Compare Grote, Hist. of Gr., vol. i. pp. 498, 499.

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technical terms, which have a popular acceptation in common discourse as well as a precise scientific import. Since (he says) they have a meaning in common language, a careless reader is prone to disregard the technical limitation of this meaning, and to attempt to collect their import in scientific books, in the same vague and conjectural manner in which he collects the purpose of words in common cases. Hence the language of science, when thus resembling common language, is liable to be employed with an absence of that scientific precision which alone gives it value. Popular writers and talkers, when they speak of force, momentum, action, and reaction, and the like, often afford examples of the inaccuracy thus arising from the scientific appropriation of common terms." In like manner, the scientific discussions of questions in the political and ethical sciences often lose their precision and value, when all the principal terms come to be expounded according to their loose and fluctuating applications in popular language. The practical result is, that the writer on the moral sciences is nearly debarred from the use of technical terms, or that his use of them is unaccompanied with the advantage which results from them in the physical sciences. When he has affixed a precise and restricted meaning upon a term, and has framed a definition, not taken from his own arbitrary notions of clearness, but founded on an investigation of the properties of the class which it represents, his labour is vain as soon as the term comes to be employed in popular language; its precision and restriction are lost as soon as it slips from his hand, and passes into the mouths of the multitude; and the propositions into which he has introduced it, with a technical sense, become, as they are now interpreted, either pointless and unmeaning, or paradoxical and false.

The diversities of opinion generated by popular discussion are further aggravated by the rival pretensions of theorists and practicians to be considered as guides and authorities in practical affairs. Theorists, by an observation of particulars, and by generalising upon them, attempt to construct a system of scientific propositions with respect to a certain subject; upon which system a set of rules intended for the guidance of practice may be founded. These rules form an art. Many scientific investigations have been conducted, and scientific treatises composed, by persons unpractised in the corresponding art; thus, Aristotle composed a 1 Philos. of Ind. Sciences, vol. i. p. 52.

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