Turning from sense to reason, Carneades attacks the syllogistic process on grounds already specified in connexion with the earlier Sceptics; and also on the plea that to prove the possibility of syllogism is itself to syllogise, and thus involves either a petitio principii or a regress ad infinitum.[235] Such a method is, of course, suicidal, for it disproves the possibility of the alleged disproof, a consideration which the Stoics did not fail to urge, and which the later Sceptics could only meet by extending the rule of suspense to their own arguments against argument.[236] Nevertheless the sceptical analysis detected some difficulties in the ordinary theory of logic, which have been revived in modern times, and have not yet received any satisfactory solution. Sextus Empiricus, probably copying an earlier authority, it may be Carneades himself, observes that, as the major premise of every syllogism virtually contains the minor, it is either superfluous, or assumes the proposition to be proved. Thus we argue that Socrates is an animal because he is a man, and all men are animals. But if we do not know this latter proposition to be true in the case of Socrates, we cannot be sure that it is true in any case; while if we know it to be true in his case, we do not need to begin by stating it in general terms. And he also attempts to show the impossibility of a valid induction by the consideration, since so often urged, that to generalise from a limited number of instances to a whole class is unsafe, for some of the unknown instances may be contradictory, while the infinite, or at least indefinite multiplicity of individuals precludes the possibility of their exhaustive enumeration.[237]
When the Academicians pass from the form to the matter of dogmatic philosophy, their criticisms acquire greater interest and greater weight. On this ground, their assaults are principally directed against the theology of their Stoic and Epicurean rivals. It is here in particular that Carneades reveals himself to us as the Hume of antiquity. Never has the case for agnosticism been more powerfully made out than by him or by the disciples whom he inspired. To the argument for the existence of supernatural beings derived from universal consent, he replies, first, that the opinion of the vulgar is worthless, and secondly, that men’s beliefs about the gods are hopelessly at variance with one another, even the same divinity being made the subject of numberless discordant legends.[238] He reduces the polytheistic deification of natural objects to an absurdity by forcing it back through a series of insensible gradations into absolute fetichism.[239] The personification of mental qualities is similarly treated, until an hypothesis is provided for every passing mood.[240] Then, turning to the more philosophical deism of the Stoics, he assails their theory of the divine benevolence with instance after instance of the apparent malevolence and iniquity to be found in Nature; vividly reminding one of the facts adduced by Mr. Herbert Spencer in confutation of the similar views held by modern English theologians.[241] As against the whole theory of final causes, Carneades argues after a method which, though logically sound, could not then present itself with the authority which advancing science has more recently shown it to possess. ‘What you Stoics,’ he says, ‘explain as the result of conscious purpose, other philosophers, like Strato for instance, explain with equal plausibility as the result of natural causation. And such is our ignorance of the forces at work in Nature that even where no mechanical cause can be assigned, it would be presumptuous to maintain that none can exist.[242] The reign of law does not necessarily prove the presence of intelligence; it is merely the evidence of a uniform movement quite consistent with all that we know about the working of unconscious forces.[243] To contend, with Socrates, that the human mind must be derived from a Universal Mind pervading all Nature would logically involve the transfer of every human attribute to its original source.[244] And to say that the Supreme Being, because it surpasses man, must possess an intelligence like his, is no more rational than to make the same assumption with regard to a great city because it is superior to an ant.’[245]
The materialism of his dogmatic contemporaries placed them at a terrible disadvantage when the sceptical successor of Plato went on to show that eternal duration is incompatible with whatever we know about the constitution of corporeal substance; and this part of his argument applied as much to the Epicurean as to the Stoic religion.[246] But even a spiritualistic monotheism is not safe from his dissolving criticism. According to Carneades, a god without senses has no experience of whatever pleasurable or painful feelings accompany sensation, and is therefore, to that extent, more ignorant than a man; while to suppose that he experiences painful sensations is the same as making him obnoxious to the diminished vitality and eventual death with which they are naturally associated. And, generally speaking, all sensation involves a modification of the sentient subject by an external object, a condition necessarily implying the destructibility of the former by the latter.[247] So also, moral goodness is an essentially relative quality, inconceivable without the possibility of succumbing to temptation, which we cannot attribute to a perfect Being.[248] In a word, whatever belongs to conscious life being relative and conditioned, personality is excluded from the absolute by its very definition.
As to the proofs of divine agency derived from divination, they are both irrational and weak. If all things are predetermined by God’s providence, knowledge of the future is useless, and, therefore, cannot have been given to us. Moreover, no confidence can be placed in the alleged fulfilments of prophecy; probably most of them are fictitious and the remainder accidental. For the rest, good luck is distributed without regard to merit; and the general corruption of mankind shows that, from the Stoic point of view, human nature is a complete failure.[249]
Well may M. Havet say of the Academicians: ‘ce sont eux et non les partisans d’Epicure qui sont les libres penseurs de l’antiquité ou qui l’auraient voulu être; mais ils ne le pouvaient pas.’[250] They could not, for their principles were as inconsistent with an absolute negation as with an absolute affirmation; while in practice their rule was, as we have said, conformity to the custom of the country; the consequence of which was that Sceptics and Epicureans were equally assiduous in their attendance at public worship. It is, therefore, with perfect dramatic appropriateness that Cicero puts the arguments of Carneades into the mouth of Cotta, the Pontifex Maximus; and, although himself an augur, takes the negative side in a discussion on divination with his brother Quintus. And our other great authority on the sceptical side, Sextus Empiricus, is not less emphatic than Cotta in protesting his devotion to the traditional religion of the land.[251]
We have seen with what freedom Carneades discussed the foundations of morality. It is now evident that in so doing he did not exceed the legitimate functions of criticism. No one at the present day looks on Prof. Bain and Mr. Henry Sidgwick as dangerous teachers because they have made it clear that to pursue the greatest happiness of the greatest number is not always the way to secure a maximum of happiness for oneself. The really dangerous method, as we now see, is to foster illusions in early life which subsequent experience must dispel.
With the introduction of practical questions, we pass to the great positive achievement of Carneades, his theory of probable evidence. Intended as an account of the process by which belief is adjusted to safe action rather than of the process by which it is brought into agreement with reality, his logic is a systematisation of the principles by which prudent men are unconsciously guided in common life. Carneades distinguishes three degrees of probability. The lowest is attached to simple perception. This arises when we receive the impression of an object without taking the attendant circumstances into account. The next step is reached when our first impression is confirmed by the similar impressions received from its attendant circumstances; and when each of these, again, bears the test of a similar examination our assurance is complete. The first belief is simply probable; the second is probable and uncontradicted; the third probable, uncontradicted, and methodically established. The example given by Sextus is that of a person who on seeing a coil of rope in a dark passage thinks that it may be a snake, and jumps over it, but on turning round and observing that it remains motionless feels inclined to form a different opinion. Remembering, however, that snakes are sometimes congealed by cold in winter, he touches the coil with his stick, and finally satisfies himself by means of this test that the image present to his mind does not really represent a snake. The circumstances to be examined before arriving at a definite judgment include such considerations as whether our senses are in a healthy condition, whether we are wide awake, whether the air is clear, whether the object is steady, and whether we have taken time enough to be sure that the conditions here specified are fulfilled. Each degree of probability is, again, divisible into several gradations according to the strength of the impressions received and the greater or less consilience of all the circumstances involved.[252]
The Academic theory of probability bears some resemblance to the Canonic of Epicurus, and may have been partially suggested by it. Both are distinguished from the Aristotelian and Stoic logic by the care with which they provide for the absence of contradictory evidence. In this point, however, the superiority of Carneades to Epicurus is very marked. It is not enough for him that a present impression should suggest a belief not inconsistent with past experience; in the true inductive spirit, he expressly searches for negative instances, and recommends the employment of experiment for this purpose. Still more philosophical is the careful and repeated analysis of attendant circumstances, a precaution not paralleled by anything in the slovenly method of his predecessor. Here the great value of scepticism as an element in mental training becomes at once apparent. The extreme fallibility of the intellectus sibi permissus had to be established before precautions could be adopted for its restraint. But the evidence accepted in proof of this fallibility has been very different at different times, and has itself given rise to more than one fallacious interpretation. With us it is, for the most part, furnished by experience. The circumstance that many demonstrable errors were formerly received as truths is quite sufficient to put us on our guard against untested opinions. With Bacon, it was not the erroneousness of previous systems, but their barrenness and immobility, which led him to question the soundness of their logic; and his doubts were confirmed by an analysis of the disturbing influences under which men’s judgments are formed. The ancient Sceptics were governed entirely by à priori considerations. Finding themselves confronted by an immense mass of contradictory opinions, they argued that some of these must be false as all could not possibly be true. And an analysis of the human faculties led them, equally on à priori grounds, to the conclusion that these irreconcilable divergences were but the result and the reproduction of an interminable conflict carried on within the mind itself. They could not foresee how much time would do towards reducing the disagreement of educated opinion within a narrower compass. They did not know what the experience of experience itself would teach. And their criticisms on the logic and metaphysics of their opponents were rendered inconclusive, as against all certainty, by the extent to which they shared that logic and metaphysics themselves. Carneades, at least, seems to assume throughout that all existence is material, that there is a sharp distinction between subject and object in knowledge, and that there is an equally sharp distinction between sensation and reasoning in the processes by which knowledge is obtained. In like manner, his ethical scepticism all turns on the axiom, also shared by him with the Stoics, that for a man to be actuated by any motive but his own interest is mere folly.
Modern agnosticism occupies the same position with regard to the present foundation and possible future extension of human knowledge as was occupied by the ancient Sceptics with regard to the possibility of all knowledge. Its conclusions also are based on a very insufficient experience of what can be effected by experience, and on an analysis of cognition largely adopted from the system which it seeks to overthrow. Like Scepticism also, when logically thought out, it tends to issue in a self-contradiction, at one time affirming the consciousness of what is, by definition, beyond consciousness; and at another time dogmatically determining the points on which we must remain for ever ignorant. It may be that some problems, as stated by modern thinkers, are insoluble; but perhaps we may find our way our of them by transforming the question to be solved.
If, in the domain of pure speculation, contemporary agnosticism exaggerates the existing divergences, in ethics its whole effort is, contrariwise, to reduce and reconcile them. Such was also the tendency of Carneades. He declared that, in their controversy about the highest good, the difference between the Stoics and the Peripatetics was purely verbal. Both held that we are naturally framed for the pursuit of certain objects, and that virtuous living is the only means by which they can be attained. But while the disciples of Aristotle held that the satisfaction of our natural impulses remains from first to last the only end, the disciples of Zeno insisted that at some point—not, as would seem very particularly specified—virtuous conduct, which was originally the means towards this satisfaction, becomes substituted for it as the supreme and ultimate good.[253] That the point at issue was more important than it seemed is evident from its reproduction under another form in modern ethical philosophy. For, among ourselves, the controversy between utilitarianism and what, for want of a better name, we must call intuitionism, is gradually narrowing itself to the question whether the pursuit of another’s good has or has not a higher value than the quantity of pleasure which accrues to him from it, plus the effects of a good example and the benefits that society at large is likely to gain from the strength which exercise gives to the altruistic dispositions of one of its members. Those who attribute an absolute value to altruism, as such, connect this value in some way or other with the spiritual welfare of the agent; and they hold that without such a gain to himself he would gradually fall back on a life of calculating selfishness or of unregulated impulse. Here we have the return from a social to an individual morality. The Stoics, conversely, were feeling their way from the good of the individual to that of the community; and they could only bridge the chasm by converting what had originally been a means towards self-preservation into an end in itself. This Carneades could not see. Convinced that happiness was both necessary and attainable, but convinced also that the systems which had hitherto offered it as their reward were logically untenable, he wished to place morality on the broad basis of what was held in common by all schools, and this seemed to be the rule of obedience to Nature’s dictates,—a rule which had also the great merit of bidding men do in the name of philosophy what they already felt inclined to do without any philosophy at all. We are told, indeed, that he would not commit himself to any particular system of ethics; the inference, however, is not that he ignored the necessity of a moral law, but that he wished to extricate it from a compromising alliance with untenable speculative dogmas. Nevertheless his acceptance of Nature as a real entity was a survival of metaphysics; and his morality was, so far as it went, an incipient return to the traditions of the Old Academy.