One important result of our habit of thus forcing the universe to become "the bond-slave of human thought" is to be found, as Bacon notes, in our proneness to "suppose the existence of more order and regularity in the world" than is actually to be discovered there. While we read design and purpose into the phenomena of Nature because we are conscious of design and purpose in our own activities, thus allowing ourselves to drift into the metaphysical doctrine of Final Causes, we also do our best to bring Nature's multitudinous operations into such definite formulas as will satisfy our love of plan and symmetry. We are not content till we can systematize and digest, whence our continual recourse to loose analogies and fanciful resemblances. We start from an imagined necessity of order, or from some conception of things attractive because of its apparent simplicity, and then reason out from this into the facts of Nature. Mill furnishes some telling examples. "As late as the Copernican controversy it was urged, as an argument in favor of the true theory of the solar system, that it placed the fire, the noblest element, in the center of the universe. This was a remnant of the notion that the order of the universe must be perfect, and that perfection consisted in conformity to rules of procedure, either real or conventional. Again, reverting to numbers, certain numbers were perfect, therefore these numbers must obtain in the great phenomena of Nature. Six was a perfect number—that is, equal to the sum of all its factors—an additional reason why there must be exactly six planets. The Pythagoreans, on the other hand, attributed perfection to the number ten, but agreed in thinking that the perfect numbers must be somehow realized in the heavens; and knowing only of nine heavenly bodies to make up the enumeration, they asserted 'that there was an antichthon, or counter-earth, on the other side of the sun, invisible to us.' Even Huygens was persuaded that when the number of heavenly bodies had reached twelve it could not admit of any further increase. Creative power could not go beyond that sacred number."[20] Do these concrete illustrations of perverse reasoning strike us as ludicrous? It is because they are taken from an order of ideas long since outgrown. The tendencies they exemplify have not been outgrown. We have only to keep a vigilant eye on our own mental conduct to be convinced that we are very apt to begin with some general notion of "the fitness of things," or what "ought to be," and to argue thence to conclusions not a whit less absurd essentially than those just referred to.
While these universal mental habits are conspicuous enough in the higher regions of thought and begin to play tricks with us the moment we undertake on our own accounts any serious speculation, there are other Idols of the Tribe whose influence is perhaps more commonly fatal. We all jump at conclusions, the mind feigning and supposing "all other things to be somehow, though it can not see how, similar to those few things by which it is surrounded"; we all allow ourselves to be unduly "moved by those things most which strike and enter the mind simultaneously and suddenly, and so fill the imagination." Hasty judgments are thus daily and hourly passed on men and things, and rash generalizations permitted to circulate untested. Even more disastrous, perhaps, in the long run, is the power of prepossessions. When once, says Bacon, the human understanding has "adopted an opinion (either as being the received opinion, or as being agreeable to itself)" it straightway "draws all things else to support and agree with it." Illustrations may be found in every direction. Note, for instance, the vitality, even in the teeth of positive disproof, of many long-accepted and often-challenged ideas—belief in dreams, omens, prophecies, in providential visitations and interpositions, in the significance of coincidences, in popular saws about natural phenomena, in quacks and quackery, in old wives' tales, vulgar and pseudo-scientific. The story of witchcraft is only another example of the same kind, though written large in the chronicles of the world in letters of fire and blood; the human understanding had "adopted" a belief in witches, and drew "all things else to support and agree with it." In all such cases of prepossession the mind obstinately dwells on every detail that favors its accepted conclusions, while disregarding or depreciating everything that tells against them; it is always, in Bacon's phrase, "more moved and excited by affirmatives than by negatives." Thus, we hear much of the one dream that is fulfilled, and of the ninety and nine that are unfulfilled—nothing. Bacon illustrates this perversity by the well-known anecdote of the ancient cynic, which may be left to convey its own moral: "And therefore it was a good answer that was made by one who, when they showed him hanging in a temple a picture of those who had paid their vows as having escaped shipwreck, and would have him say whether he did not now acknowledge the power of the gods—'Ay,' asked he again, 'but where are they painted that were drowned after their vows?'"
Finally, among these Idols of the Tribe we must include the disturbance caused by the play of feeling upon the mind. "The human understanding is no dry light, but receives an infusion from the will and affections, whence proceed sciences which may be called 'sciences as one would.'" We all know, to our cost, how passion will warp judgment; how difficult it is to see clearly when the emotions are thoroughly aroused; how tenaciously men cling to opinions they are familiar with, or would fain have to be true; how fiercely they contest ideas that are unfamiliar or repugnant. Had it been contrary to the interest of authority, observed shrewd old Hobbes, that the three angles of a triangle should be equal to two angles of a square, the fact would have been, if not disputed, yet suppressed.[21] Similarly, if the passions of men had been called into play over the most clearly demonstrable of abstract mathematical truths, we may be sure that furious controversy would have attended the issue, and some way found to overthrow the demonstration. That two and two make four would have been denied had any strong emotion been excited against the proposition. "Men," said Whateley, "are much more anxious to have truth on their side than to be on the side of truth." And the danger is greater because we are frequently not aware of the bias given by feeling. There are cases in plenty where men more or less consciously and deliberately espouse "sciences as one would," but there are many others in which the emotional interference is insidious and obscure. "Numberless, in short, are the ways, and sometimes imperceptible, in which the feelings color and infect the understanding."
These Idols of the Tribe are of course inherent in our intellectual constitution, and are ineradicable. The simple consideration that all knowledge is relative—that by no effort and under no circumstances can we escape beyond the conditions and limitations of our own minds—suffices to show that intelligence must ever mix up its own nature with the nature of things, though this fact need not make us doubt the validity of knowledge as is sometimes hastily inferred. For the rest, clear recognition of these common obstacles to thought should put us in the way of anticipating and withstanding their more serious effects. In practice it must be our object to maintain watchfulness and a careful skepticism; to test evidence and check passion; to cultivate candor, flexibility, and alertness of mind; to avoid loose generalizations; and to be ever ready to accept, revise, reject. Above all must we steadily resist the seductions of what is called common sense, and overcome that mental inertness which too often leads us to drift unthinking along the current of popular opinion.[22]
But, in addition to errors arising from the common intellectual nature of men, there are others, the sources of which are to be found in the idiosyncrasies of the individual mind. These Bacon calls Idols of the Cave;[23] for every one, he says, "has a cave or den of his own, which refracts and discolors the light of Nature, owing either to his own proper and peculiar nature; or to his education and conversation with others; or to his reading of books, and the authority of those whom he esteems and admires; or to the differences of impressions, accordingly as they take place in a mind preoccupied and predisposed, or in a mind indifferent and settled; and the like." This summary is comprehensive enough to indicate the character and point to some of the causes of individual aberrations of judgment; that it does no more than this is due to the simple fact that the personal bias is as varied as humanity itself, and that the deflecting impulses in any given case are to be referred to a complex of factors almost eluding analysis. To follow this part of the subject into detail would, therefore, manifestly be impossible. But certain of the larger and more widely influential of these disturbing forces may be roughly marked out by way of illustration.
In the first place, there is what we may call the professional bias. Exclusive devotion to separate lines of activity, study, or thought inevitably gives the mind a particular set or twist. Bacon complains that Aristotle, primarily a logician, made his natural philosophy the slave of his logic. Few specialists can escape the insulation consequent upon living too continuously in a confined area of problems and ideas. Their intellectual outlook is necessarily circumscribed, facts are seen by them out of proper perspective, and one-sidedness of training and discipline renders their judgment of things partial and incomplete. The lawyer carries his legal, the theologian his theological, the scientist his scientific bent of mind into every inquiry; with what grotesque results is only too frequently apparent. Accustomed to move in a single narrow groove, and wholly absorbed in the contemplation of certain isolated classes of phenomena, they unconsciously allow their particular interests to dominate their thought, and impose disastrous restrictions upon their view of whatever lies outside their own chosen field.
Secondly, we have the bias of nation, rank, party, sect. Here the mental disturbances are too numerous to permit and too obvious to require special exemplification. Intellectual provincialism of any kind is fatal to large and fertile thought, alike by limiting the range of our knowledge and sympathies and by inducing mental habits and implanting prejudices which prevent us from seeing things in wide relations and under a clear light. So long as our point of view is simply that of our country, our class, our party, or our church, so long, it is evident, our minds will lack the breadth and flexibility necessary for free inquiry, fruitful comparisons, sane and balanced judgments.[24]
Finally, among the Idols of the Cave "which have most effect in disturbing the clearness of the understanding," mention must be made of the temperamental bias. Every man, it has been said, is born Platonist or Aristotelian; it is certain that the great divisions in thought—religious, philosophical, political—answer roughly to fundamental differences in human nature, and that every one not checked or turned aside by extraneous influences will spontaneously gravitate in one or another direction. Bacon is only recording a fact of the commonest experience when he says that "there are found some minds given to an extreme admiration of antiquity, others to an extreme love and appetite for novelty, but few so duly tempered that they can hold the mean, neither carping at what has been well laid down by the ancients nor despising what is well introduced by the moderns." Many instinctively brace themselves against authority and tradition; by others again, whatever is handed down to us by authority and tradition is for this reason alone treated with contempt. That the crowd believes a thing is enough to convince this man of its truth, and that of its falsehood.
"The vulgar thus through imitation err;
As oft the learned by being singular."
These and similar congenital differences in men's intellectual constitutions might be illustrated indefinitely if it were necessary. A further remark of Bacon's must, however, be quoted, for it goes deeper in mental analysis and touches a less obvious point. "There is one principal and, as it were, radical distinction between different minds in respect of philosophy and the sciences, which is this: that some minds are stronger and apter to mark the differences of things, others to mark their resemblances. The steady and acute mind can fix its contemplations and dwell and fasten on the subtlest distinctions; the lofty and discursive mind recognizes and puts together the finest and most general resemblances." Men belonging to the former class we should call logical and critical; those belonging to the latter, imaginative and constructive. Each class tends to the excesses of its own predominant powers, and in each case excess interferes with calm reasoning and sound judgment.