1. Scientific Methodology - Deductive Reasoning and Self-Refuting Arguments
It is a major mistake to consider Epicurus to be a simple "empiricist" who holds that the senses alone are the tests of truth. Epicurus relied heavily on deductive reasoning. It is impossible to observe atoms or void directly, so we must deduce their existence from things that we do perceive. Similarly, it is impossible to observe abstract concepts directly, so we must make deductions about them using the concrete examples which are perceivable to us. Epicurus does not denounce logic or reason at all, but he insists that their conclusions must be grounded in observations which can be validated by the senses, anticipations, and feelings.
A distinctive feature of Epicurean scientific methodology is the doctrine of multiple explanations. For phenomena we can directly test -- such as whether atoms exist, whether void exists, whether all things come from seeds -- the evidence points to a single correct answer and we should embrace it firmly. But for phenomena we cannot directly test from our position -- such as the exact cause of a particular celestial event -- Epicurus held that we should accept all explanations that are consistent with observable facts, without insisting on one to the exclusion of others. This is not intellectual laziness but therapeutic reasoning: the anxiety that comes from committing to a single explanation of celestial events, when that explanation might be wrong, is groundless. The point of studying celestial phenomena is not to satisfy academic curiosity but to free ourselves from the fear that the gods cause them. Any natural explanation achieves that therapeutic goal, so we need not fight over which one is correct.
We must observe that even in celestial inquiry we should not assume any mode of investigation other than that suited to the investigation of natural science in general. But in respect of those things which admit of several modes of explanation consistent with the phenomena, we must not assume for them a single mode of explanation, but allow for each a multiplicity of them. For they do not achieve the same result as the person who combines both things -- investigation of things in the heavens above, and also examination of what falls out thus -- and who does not know by what means this can occur. (Bailey)
First, we should not think that any other end is served by knowledge of celestial events, whether they be discussed in a context or in isolation, than freedom from disturbance and firm confidence, just as in the other areas of discourse. And neither should we force through what is impossible, nor should we in all areas keep our study similar either to discourses on the conduct of life or to those belonging to the solution of the other problems of physics, for example that the totality of things is body and intangible substance, or that there are atomic elements, and all the theses of this kind which are uniquely consistent with things evident. In the case of celestial events this is not the case: both the causes of their coming to be and the accounts of their essence are multiple. For physics should not be studied by means of empty judgments and arbitrary fiat, but in the way that things evident require. What our life needs is not private theorizing and empty opinion, but an untroubled existence. Now in respect of all things which have a multiplicity of explanations consistent with things evident, complete freedom from trepidation results when someone in the proper way lets stand whatever is plausibly suggested about them. But when someone allows one explanation while rejecting another equally consistent with what is evident, he is clearly abandoning natural philosophy altogether and descending into myth. Signs relating to events in the celestial region are provided by certain of the things familiar and evident -- things whose mode of existence is open to view -- and not by things evident in the celestial region. For these latter are capable of coming to be in multiple ways. We must, nevertheless, observe our impression of each one; and we must distinguish the events which are connected with it, events whose happening in multiple ways is uncontested by familiar events. (tr. Long & Sedley)
Let us now sing what are the causes of the heavenly bodies' motions. First, if the great sphere of the sky rotates, we must say that the air exerts pressure on its pole at each end, and holds it imprisoned from both sides; and that then other air flows above and travels in the direction in which the shining stars of the fixed heavens rotate; or else other air flows below, and pushes the sphere up in the opposite direction, just as we see rivers turn water-wheels and their scoops. Another possibility that the sky as a whole is stationary while the bright heavenly bodies move: whether because fast aether currents, trapped within the world, go round seeking an outlet and spin fires all through the nocturnal zone of the sky; or because air flowing from somewhere else, outside the world, drives the fires to rotate; or because they themselves have the power to edge forward in the direction in which their food entices them as they travel, pasturing their fiery bodies all through the sky. For it is hard to state with certainty which of these is the case in our world. But what I am expounding is what is possible, and happens in the various worlds variously formed throughout the universe, and my procedure to set out a plurality of causes which are able to be those of the motions of the heavenly bodies throughout the universe. Of them, one must also be the cause which gives the heavenly bodies their power of motion in our world. But it is not the job of one who proceeds with caution to lay down which of them it is. (tr. Long & Sedley)
There are also a number of things of which it is not enough to name one cause, but rather many causes, one of which will however be the actual one -- just as, if you were yourself to see at a distance the dead body of a man, it would be appropriate to list all the causes of death, so as to include the specific cause of his death. For you would not be able to establish that he had died by the sword, from cold, from disease, or by poison; yet we know that it was something of this kind that happened to him. And likewise in many other matters we are in a position to say the same. (tr. Long & Sedley)
For granted that 'If the first, then the second' is true whenever 'If not the second, not the first either' is true, it does not therefore follow that only the Elimination Method is cogent. For 'If not the second, not the first either' comes out true sometimes in as much as, when the second is hypothetically eliminated, by its very elimination the first is eliminated too -- as in 'If there is motion, there is void', since, when void is hypothetically eliminated, by its mere elimination motion will be eliminated too, so that such a case fits the elimination type -- but sometimes not in this way but because of the very inconceivability of the first being, or being of this kind, but the second not being, or not being of this kind. For instance, 'If Plato is a man, Socrates is a man too.' For given that this is true, 'If Socrates is not a man, Plato is not a man either' comes out true as well, not because by the elimination of Socrates Plato is co-eliminated, but because it is impossible to conceive of Socrates not being a man but Plato being a man. And that belongs to the Similarity Method. (tr. Long & Sedley)
Those who attack sign-inference by similarity do not notice the difference between the aforementioned [senses of 'in so far as'], and how we establish the 'in so far as' premise, such as, for instance, that man in so far as he is man is mortal.... For we establish the necessary connection of this with that from the very fact that it has been an observed concomitant of all the instances which we have encountered, especially as we have met a variety of animals belonging to the same type which while differing from each other in all respects share such-and-such common characteristics. Thus we say that man, in so far as and in that he is man, is mortal, because we have encountered a wide variety of men without ever finding any variation in this kind of accidental attribute, or anything that draws us towards the opposite view. So this is the method on which the establishment of the premise rests, both for this issue and for the others in which we apply the 'in so far as' and 'in that' construction -- the peculiar connection being indicated by the fact that the one thing is the inseparable and necessary concomitant of the other. The same is not true in the case of what is established merely by the elimination of a sign. But even in these cases, it is the fact that all the instances which we have encountered have this as their concomitant that does the job of confirmation. For it is from the fact that all familiar moving objects, while having other differences, have it in common that their motion is through empty spaces, that w e conclude the same to be without exception true also in things non-evident. And our reason for contending that if there is not, or has not been, fire, smoke should be eliminated, is that smoke has been seen in all cases without exception to be a secretion from fire. (6) Another error which they make is in not noticing our procedure of establishing that no obstacle arises through things evident. For the existence of chance and of that which depends on us is not sufficient ground for accepting the minimal swerves of atoms: it is necessary to show in addition that nothing else self-evident conflicts with the thesis. (tr. Long & Sedley)
[Above: Long & Sedley excerpt. Below: the same passage in Bailey's translation.]
Opinion they also call 'supposition', and they say that it is true and false. If it is attested or uncontested, it is true; if it is unattested or contested, it comes out false. Hence their introduction of that which awaited - for example, waiting and getting near the tower and learning how it appears from near by. (tr. Long & Sedley)
Of opinions, then, according to Epicurus, some are true, some false. True are those attested and those uncontested by self-evidence; false are those contested and those unattested by self-evidence. Attestation is perception through a self-evident impression of the fact that the object of opinion is such as it was believed to be. For example, if Plato is approaching from far off, I form the conjectural opinion, owing to the distance, that it is Plato. But when he has come close, there is further testimony that he is Plato, now that the gap is reduced, and it is attested by the self-evidence itself. Non-contestation is for that which is evident to follow from the non-evident thing posited and believed. For example, Epicurus, in saying that there is void, which is non-evident, confirms this through the self-evident fact of motion. For if void does not exist, there ought not to be motion either, since the moving body would lack a place to pass into as a result of everything's being full and solid. Therefore the non-evident thing believed is uncontested by that which is evident, since there is motion. Contestation, on the other hand, is something which conflicts with non-contestation. For it is the elimination of that which is evident by the positing of the non-evident thing. For example, the Stoic says that void does not exist, judging something non-evident; but once this is posited about it, that which is evident, namely motion, ought to be co-eliminated with it. For if void does not exist, necessarily motion does not occur either, according to the method already demonstrated. Likewise, too, non-attestation is opposed to attestation, being confrontation through self-evidence of the fact that the object of opinion is not such as it was believed to be. For example, if someone is approaching from far off, we conjecture, owing to the distance, that he is Plato. But when the gap is reduced, we recognize through self-evidence that it is not Plato. That is what non-attestation is like: the thing believed was not attested by the evident. Hence attestation and non-contestation are the criterion of something's being true, while non-attestation and contestation are the criterion of its being false. And self-evidence is the foundation and basis of everything. (tr. Long & Sedley)
[Above: Long & Sedley excerpt. Below: the same passage in full surrounding context, tr. Bury, Loeb , Against the Logicians I.208-215.]
- Page scan: Sextus Empiricus, Against the Professors 211-216 (tr. Long & Sedley), page 1
- Page scan: Sextus Empiricus, Against the Professors 211-216 (tr. Long & Sedley), page 2
- Page scan: Sextus Empiricus, Against the Logicians I.208-215 (tr. Bury, Loeb)
- Page scan: Sextus Empiricus, Against the Logicians I.211-216 (tr. Bury, Loeb)
But Demetrius the Laconian, one of the notables of the Epicurean School, used to declare that this sort of objection is easy to dispose of, "for," says he, "when we have established one of the particular proofs (for example, that which deduces that indivisible elements exist, or that void exists) and shown that it is sure, we shall at once have secured, as included in this, the trustworthiness of generic proof; for where there exists the particular of a genus, there we certainly find also the genus of which it is the particular." (Bury)
2. Dialectical Logic And Academic / Logical Skepticism Cannot Determine Truth
Epicurus rejected the use of dialectical logic -- the method of purely abstract argumentation developed by Plato and refined by the Stoics and Academics -- as a self-sufficient path to truth. His objection was not that logic and argument have no role in philosophy, but that formal argumentation, when disconnected from the evidence of the senses, becomes a tool for generating any conclusion the arguer wants rather than a reliable path to reality. The Stoics and Academic philosophers placed enormous confidence in the power of deductive chains of reasoning to establish philosophical conclusions; Epicurus countered that any argument whose premises cannot be grounded in reliable sensory evidence is worthless as a guide to truth, no matter how formally valid the deduction. In Cicero's report, Torquatus notes that Epicurus "judged that the logic of your school possesses no efficacy either for the amelioration of life or for the facilitation of debate" -- precisely because it floated free of the evidence that could test it.
Radical skepticism -- the position that nothing at all can be known with certainty -- receives the same rejection but on different grounds. As discussed in B-1, radical skepticism is self-defeating: the person who asserts it cannot even assert it coherently. But beyond self-refutation, radical skepticism is practically catastrophic: if no reliable knowledge is possible, then no deliberation, no ethical judgment, no philosophical investigation can even begin. Diogenes of Oinoanda observed that those who assert that things are inapprehensible are, in effect, saying that natural science is unnecessary -- for who would pursue knowledge they believe can never be found? Epicurus' response was that the evidence of the senses, anticipations, and feelings is sufficient for the knowledge we actually need to live well, and that uncertainty about remote or speculative matters does not justify abandoning confidence in what our natural faculties reliably report.
Note that the Four Principles of Academic Skepticism in Book 2 of Academic Questions:
1 - There Are Some False Appearances
2 - A False Appearance Cannot Be Perceived
3 - As to appearances which appear the same, it is not possible through the senses to grasp as true some but not others.
4 - For every true impression there also a false impression, so no impression is securely graspable
If you fight against all your sensations, you will not have a standard against which to judge even those of them you say are mistaken. (tr. Long & Sedley)
If you are going to reject any sensation absolutely, and not distinguish opinions reliant on evidence yet awaited from what is already present through sensation, through feelings, and through every focusing of thought into an impression, you will confound all your other sensations with empty opinion and consequently reject the criterion in its entirety. And if you are going to treat as established both all the evidence yet awaited in your conjectural conceptions, and that which has failed to earn attestation, you will not exclude falsehood, so that you will have removed all debate and all discrimination between correct and incorrect. (tr. Long & Sedley)
They [the Epicureans] reject dialectic as superfluous, saying that it is sufficient that natural philosophers should proceed in accordance with the words belonging to things. (tr. Long & Sedley)
These facts, he thinks, are perceived by the senses, as that fire is hot, snow white, honey sweet, none of which things need be proved by elaborate argument: it is enough merely to draw attention to them. For there is a difference, he holds, between formal syllogistic proof of a thing and a mere notice or reminder: the former is the method for discovering abstruse and recondite truths, the latter for indicating facts that are obvious and evident. Strip mankind of sensation, and nothing remains; it follows that Nature herself is the judge of what is in accordance with or contrary to nature. (tr. Long & Sedley)
[Above: Long & Sedley excerpt. Below: the same passage in context, tr. Rackham, De Finibus I.30.]
We must firmly grasp a well-established scientific system, observing the standard or Canon that has fallen as it were from heaven, so that all men may know it -- making that Canon the test of all our judgments -- that we can hope always to stand fast in our belief, unshaken by the eloquence of any man. (tr. Long & Sedley)
[Above: Long & Sedley excerpt. Below: the same passage in context, tr. Yonge, De Finibus I.63.]
For if some of the physicists, like Democritus, have abolished all phenomena, and others, like Epicurus and Protagoras, have established all, while others again, like the Stoics and Peripatetics, have abolished some and established others,--then, whether one assumes as criterion the intellect or the sense or both together, in every case it is by all means necessary that either some apparent or some non-evident thing should be adopted to judge between these thinkers.
[Editorial note, not part of the Sextus text: among these three positions, Epicurus alone affirmed all sensory appearances as reliable without exception -- the most thoroughgoing defense of the veracity of sense experience among the major schools.]
Now, if someone thinks that nothing is known, one thing he doesn't know is whether that can be known, since he admits to knowing nothing... You will find that the preconception of true has its origin in the senses, and that the senses cannot be refuted. For something of greater reliability must be found, something possessing the intrinsic power to convict falsehoods with truths. Well, what should be considered to have greater reliability than the senses? Will reason have the power to contradict them, if it is itself the product of false sensation? For reason is in its entirety the product of the senses, so that if the senses are not true all reason becomes false as well... Hence you will find that the entire battalion of words which has been marshaled and armed against the senses is futile. Lastly, just as in a building, if the yardstick is defective at the outset, if the set square is misleading for lack of straight edges, and if the level has the slightest wobble anywhere in it, the inevitable result is that the whole house is made wrongly -- crooked, distorted, bulging backwards and forwards, misproportioned. So too you will find that any account of the world must be distorted and false if it is based upon the falsity of the senses. (tr. Long & Sedley)
Fr. 4 ... [as is supposed by] some of the philosophers and especially the Socratics. They say that pursuing natural science and busying oneself with investigation of celestial phenomena is superfluous and unprofitable. Fr. 5 Others do not explicitly stigmatize natural science as unnecessary, being ashamed to acknowledge this, but use another means of discarding it. For, when they assert that things are inapprehensible, what else are they saying than that there is no need for us to pursue natural science? After all, who will choose to seek what he can never find? (tr. Long & Sedley)
[Not specifically Epicurean, but a Skeptic's own admission that the evidence of the senses defeats dialectical arguments against plain facts.]
However, it is a matter of indifference whether motion is apprehended chiefly by sense or by intellect; for it is plain that the evidence of facts seems to bear out the view that motion exists. And for this reason the Dogmatic philosophers are in the habit of using no other means than this to put the Doubters to shame. For, say they, if motion does not exist how does the sun run its own special course from its rising to its setting? ... And how is it that the Doubter who abolishes motion goes forth from his house in the morning and, after transacting some ordinary business, returns to it again? For all these are irrefutable signs of motion. Hence also one of the ancient Cynics, when the arguments against motion were propounded to him, made no reply at all but stood up and walked about, thus flouting the folly of the sophist by the evidence of actual fact. (Bury)