Evidently these principles, which so are made to serve as standards of validity in law and custom, knowledge and belief, are of the nature of canons, established rules, and have the authority of precedent, prescription. They have been defined by the attrition of use and wont and disputation, and they are accepted in a somewhat deliberate manner by common consent, and are upheld by a deliberate public opinion as to what is right and seemly. In the popular apprehension, and indeed in the apprehension of the trained jurists and scholars for the time being, these constituent principles of the accepted point of view are "fundamentally and eternally right and good." But this perpetuity with which they so are habitually invested in the popular apprehension, in their time, is evidently such a qualified perpetuity only as belongs to any settled outgrowth of use and wont. They are of an institutional character and they are endowed with that degree of perpetuity only that belongs to any institution. So soon as a marked change of circumstances comes on, -- a change of a sufficiently profound, enduring and comprehensive character, such as persistently to cross or to go beyond those lines of use and wont out of which these settled principles have emerged, -- then these principles and their standards of validity and finality must presently undergo a revision, such as to bring on a new balance of principles, embodying the habits of thought enforced by a new situation, and expressing itself in a revised scheme of authoritative use and wont, law and custom. In the transition from the medieval to the modern point of view, e. g., there is to be seen such a pervasive change in men's habitual outlook, answering to the compulsion of a new range of circumstances which then came to condition the daily life of the peoples of Christendom. In this mutation of the habitual outlook, between medieval and modern times, the contrast is perhaps most neatly shown in the altered standards of knowledge and belief, rather than in the settled domain of law and morals. Not that the mutation of habits which then overtook the Western world need have been less wide or less effectual in matters of conduct; but the change which has taken effect in science and philosophy, between the fourteenth century and the nineteenth, e. g., appears to have been of a more recognizable character, more easily defined in succinct and convincing terms.
It has also quite generally attracted the attention of those men who have interested themselves in the course of historical events, and it has therefore become something of a commonplace in any standard historical survey of modern civilisation to say that the scheme of knowledge and belief underwent a visible change between the Middle Ages and modern times.
It will also be found true that the canons of knowledge and belief, the principles governing what is fact and what is credible, are more intimately and intrinsically involved in the habitual behavior of the human spirit than any factors of human habit in other bearings. Such is necessarily the case, because the principles which guide and limit knowledge and belief are the ways and means by which men take stock of what is to be done and by which they take thought of how it is to be done. It is by the use of their habitual canons of knowledge and belief, that men construct those canons of conduct which serve as guide and standards in practical life. Men do not pass appraisal on matters which lie beyond the reach of their knowledge and belief, nor do they formulate rules to govern the game of life beyond that limit.
So, congenitally blind persons do not build color schemes;
nor will a man without an "ear for music" become a master of musical composition. So also, "the medieval mind" took no thought and made no provision for those later-arisen exigencies of life and those later-known facts of material science which lay yet beyond the bounds of its medieval knowledge and belief; but this "medieval mind" at the same time spent much thought and took many excellent precautions about things which have now come to be accounted altogether fanciful, -- things which the maturer insight, or perhaps the less fertile conceit, of a more experienced age has disowned as being palpably not in accord with fact.
That is to say, things which once were convincingly substantial and demonstrable, according to the best knowledge and belief of the medieval mind, can now no longer be discerned as facts, according to those canons of knowledge and belief that are now doing duty among modern men as conclusive standards of reality. Not that all persons who are born within modern times are thereby rendered unable to know and to believe in such medieval facts, e. g., as horoscopes, or witchcraft, or gentle birth, or the efficacy of prayer, or the divine right of kings;
but, taken by and large, and in so far as it falls under the control of the modern point of view, the deliberate consensus of knowledge and belief now runs to the effect that these and other imponderables like them no longer belong among ascertained or ascertainable facts; but that they are on the other hand wholly illusory conceits, traceable to a mistaken point of view prevalent in that earlier and cruder age.
The principles governing knowledge and belief at any given time are primary and pervasive, beyond any others, in that they underlie all human deliberation and comprise the necessary elements of all human logic. But it is also to be noted that these canons of knowledge and belief are more immediately exposed to revision and correction by experience than the principles of law and morals. So soon as the conditions of life shift and change in any appreciable degree, experience will enforce a revision of the habitual standards of actuality and credibility, because of the habitual and increasingly obvious failure of what has before habitually been regarded as an ascertained fact.
