316. I believe the expression common sense to denote a law of our mind, apparently differing according to the different cases to which it applies, but in reality and apart from its modifications, only one, always the same, consisting in a natural inclination of our mind to give its assent to some truths not attested by consciousness nor demonstrated by reason, necessary to all men in order to satisfy the wants of sensitive, intellectual, and moral life.
If the fact be agreed on, the name is of little moment: whether common sense be or be not the most adequate to signify it, is a philological, not a philosophical, question. What we have to do, is to inquire if this inclination of which we have spoken, really exists, under what forms it is presented, to what cases it is applicable, and how far, and to what degree it may be considered a criterion of truth.
Evidently this inclination cannot, in the complication of the acts and faculties of our soul, and in the multitude and diversity of the objects offered to it, always be presented with the same character; it must undergo various modifications capable of causing it to be considered as a distinct fact, although in reality still the same, transformed in a suitable manner. The best means of avoiding a confusion of ideas, will be to designate the various cases in which the exercise of this inclination occurs.
317. We at once detect it in the case of truths immediately evident. The understanding neither does nor can prove them, and yet it must assent to them, or perish like a flame that has nothing to feed upon. The possession of one or more of these primitive truths is an indispensable condition to intellectual life; without them intelligence is an absurdity. Here, then, we find all that is comprised in the definition of common sense: the impossibility of proof; an intellectual necessity, which must be satisfied by assent; and an irresistible and universal inclination to give this assent.
Is there any objection to calling this inclination common sense? For myself, I shall not dispute upon words; I mark the fact, and this is all I need do in philosophy. I grant that the inclination to assent is not, in treating of immediate evidence, usually called common sense, and this not without a reason. In order that the word sense may be properly applied to it, the understanding ought to feel rather than know: but in immediate evidence it knows rather than feels. However this may be, I repeat that the name is of no account; yet, it would not be difficult to find this criterion of truth called by grave authors common sense. What I wish is to establish this law of our nature inclining us to give our assent to certain truths, independently of consciousness and ratiocination.
318. Not immediate evidence alone has this irresistible inclination in its favor; mediate evidence also has it. Our understanding necessarily assents, not only to first principles, but also to all propositions clearly connected with them.
The natural inclination to assent is not limited to the subjective value of ideas; it also extends to their objective value. We have already seen that this objectiveness is not directly demonstrable a priori, and yet we stand in need of it. If our understanding is not to be limited to a purely ideal and subjective world, we must know not only that things seem to us, as they do with mediate or immediate evidence, but also that they really are such as they seem to be. It is then necessary to assent to the objectiveness of ideas, and we find within ourselves an irresistible and universal inclination to such an assent.
319. What we have said of immediate and mediate evidence relatively to the objective value of ideas, is true, not only in the purely intellectual, but also in the moral order. The soul, endowed as it is with free will, needs rules for its direction: if first intellectual principles are necessary in order to know, moral principles are not less so in order to will and work. What truth and error are to the understanding, good and evil are to the will. Besides the life of the understanding, there is a life of the will; the one, without principles on which to rest, is annihilated; the other, as a moral being, perishes, or becomes an inconceivable absurdity, if it have no rule, the observation or violation of which constitutes its perfection or imperfection. Here is another necessity for the assent to certain moral truths, and another reason of this irresistible and universal inclination to assent.
I would here remark, that as it is not enough in the intellectual order to know, but it is also necessary to act, and one of the principles of action is perception by the senses; so moral truths are not only known but felt. When they are offered to the mind the understanding assents to them as unshaken, and the heart embraces them with enthusiasm and love.
320. Sensations considered as purely subjective do not meet the wants of sensitive life. We must be sure that our sensations correspond to an external world, real and true, not phenomenal. Men do not ordinarily possess either the capacity or the time requisite to investigate the philosophical questions of the existence of bodies, and to decide for or against Berkeley and his followers. What is necessary is perfect certainty that bodies do exist, that sensations have an external object in reality. All men have this certainty when they assent with an irresistible force to the objectiveness of ideas, that is, to the existence of bodies.
321. Faith in human authority furnishes us with another case of this wonderful instinct. Both the individual and society require faith: without it society and family would be impossible; the individual would be condemned to isolation, and, therefore, to death. The speech of man, the human race itself, would disappear were it not for faith. This belief has distinct grades according to different circumstances, but it always exists; man is inclined, by a natural instinct, to believe his fellow man. When many men speak, and none raise their voices against them, the force of this inclination increases in the same proportion as the number of witness, until it becomes irresistible. Who doubts the existence of Rome? And yet, the greater part of us only know it upon the authority of other men.
What foundation has faith in human authority? Most men are ignorant of the philosophical reasons which may be assigned; but their faith is not therefore less lively than that of philosophers. But why is this so? Because there is a necessity, and at its side an instinct to be satisfied. Man must believe in man, and he believes. And here note well, that the greater the necessity, the greater the faith. The very ignorant and imbecile believe all that is told them; they make other men their guide, and blindly follow them. The tender child, knowing nothing, abandons itself to the absolute belief of the greatest marvels: the word of those around is to it an invaluable criterion of truth.
322. Besides the cases of first intellectual and moral principles, the objectiveness of ideas and sensations, the weight of human authority, man must give his instantaneous assent to certain truths, which, although he might, had he the time, demonstrate, he cannot now, because so suddenly are they presented to him, that they exact an immediate formation of judgment, and, sometimes, also action. In all these cases, there is a natural inclination impelling us to assent.
Hence it is that we instinctively judge it impossible, or little less than impossible, to cause a determinate effect, by a fortuitous combination; as, for example, to form a page of Virgil by a chance mixture of types, or to hit the bull's eye of a target without taking aim, and other similar things. In this there is assuredly a philosophical reason, but one not known to common people. There is evidence of this reason in the theory of probabilities: it is a distinct application of the principle of causality, and of the natural opposition of our understanding to supposing an effect without a cause, and order where there is no ordering intelligence.
323. Arguments of analogy, are in human life necessary in infinite cases. How do we know that the sun will rise to-morrow? By the laws of nature. How do we know that these will continue in force? Evidently, we must finally recur to analogy. The sun will rise to-morrow, because it has risen to-day; it rose yesterday, and it has never failed to rise. How do we know that spring will again bring flowers, and autumn fruits? Because it has so happened in former years. Men ordinarily do not know the reasons which might be given for founding the argument from analogy on the constancy of the laws of nature, and on the relation between certain physical causes and determinate effects; but their assent is required and given.
324. In all the cases cited, excepting, perhaps, that of immediate evidence, the inclination to assent may be, and really is, called common sense. The reason of this