How We Know What We Hold To Be True
2.1[i] False religions and philosophies tell us that our senses cannot be trusted. They tell us we are too readily tricked by illusions to trust our senses. You must come to see why this argument is wrong. Illusions, such as sticks which appear bent when placed in water, occur because we deceive ourselves. We receive ourselves because we reason falsely to a hasty conclusion before we have enough evidence. We must always be on the lookout for things that interfere with our senses, and whenever we do not have a clear view we must seek out additional evidence, such as by lifting the stick from the water.
2.2 The senses do not evaluate the evidence they provide to us. Error does not arise in the senses, but in our minds, and occurs when we jump to hasty conclusions that the evidence does not truly support – when we fool ourselves into believing that we have seen things that in fact we have not seen. This is a task that is harder than most any other, but it is essential that we work to keep separate in our minds those matters that are true from those that are false and those that are doubtful.
2.3 Some men go so far as to argue that nothing can be known. These men are fools, and we should not just dismiss them as harmless, we should hold them in contempt. Why? These men admit that they know nothing, so they cannot possibly know whether their own argument is true or false. And they cannot possibly in good faith expect us to accept what they say, when they know nothing. These arguments are contemptible, and such men are in effect “placing their head where their feet should be.” It is as if, in attempting to determine whether a tower observed at a distance was round or square, they sought to “reason” an answer, rather using their feet to walk over to the tower to find out at close range.
2.4 This error will confront you in many variations, so be prepared for it: “reasoning” without evidence, or against evidence, is speculation – it is the sure path to error. The proper way to deal with men who do not accept the evidence of the senses as the highest proof possible is to decline to argue with them, and to pass them by altogether. In their blindness, such men will never accept what you say, even those things that you might point out are directly in front of them. This is our starting point: unless we trust the senses, and accept the truth of those things directly before us that our senses report clearly, it is impossible for us to obtain truth. Not by reasoning or by any other method can we find out the truth about matters that are remote and difficult, unless we first hold firmly to the truth of those things directly in front of us.
2.5 We must also ask men who argue against the senses this question: Since you have never yet seen any truth in things, how do you know what “knowing” and “not knowing” are? How have you determined that there is a difference between the true and the false, between the doubtful and the certain? Those who argue against the senses have no answer to this, because it is from the senses that comes all knowledge of the true. That which has been proved to be true through the senses cannot be refuted by “reason” alone.
2.6 Those who argue that the senses are unreliable, but yet claim they have the ability to distinguish true from false, must be able to prove their assertion through some evidence that is more persuasive. They must point to some evidence that possesses a higher certainty than the senses. But what faculty is more persuasive, what has a higher certainty, than the senses? You will often hear argument that “logic” or “reason” or “revelation” are higher than the senses. But can logic, reasoning, or revelation which are not grounded in evidence that can be verified by the senses contradict a matter which is established by senses? No! Reasoning can only be considered true when it is grounded in verifiable evidence obtained through the senses. If the senses could not be trusted to establish the truth of any matter, then even more urgently we must see that reasoning based on speculation that has no supporting evidence from the senses cannot be trusted.
2.7 Reason itself is not a faculty; it is not a sense that has its own direct connection to reality; it cannot be relied on to report truth without error, as can the senses Nature has given us. Only the accurate correspondence of words with real things enables us to advance with certainty in our studies, and reason alone, without supporting sensations, can never provide a faithful correspondence.
2.8 At times you may experience sensations that appear to contradict each other, and which you are unable to explain. For example, you may not understand at first why a tower seen at a distance appears round, but close up appears square. Rather than conclude that your lack of understanding is reason to doubt your senses, simply affirm to yourself that, at least for the moment, you do not know the reason for the discrepancy. At any time you are not able to explain a difference between sensations, the proper course is to wait before you judge and to seek out more evidence before you reach a conclusion. You must never accept an explanation that rejects one of your sensations as false. You must never accept an explanation that has no evidence to support it. You must never allow yourself to doubt the reliability of the sensations themselves. The senses report to you exactly what they observe – it is only your mind which can err by drawing improper conclusions.
2.9 The moment you fall for the mistake of doubting your senses, you have set the stage to let slip from your grasp everything which you already know to be true. This is fatal, for if you come to doubt the reliability of your senses, you will soon doubt all the conclusions you have made in your life, as all those conclusions rest on your senses. Unless you drive out this error from your mind, the foundation of everything on which your life and your existence depend will be shattered. You will lose more than just your hope of reasoning accurately. You will place your very life in jeopardy, for were you to truly give up confidence in your senses, you would have no means to see and avoid those cliffs of life, both literal and figurative, that must at all costs be avoided. All the arguments arrayed against the senses are quite without meaning, but the issue involved is critical – you will confront it in all false religions and philosophies; you must understand it; you must be prepared to defeat it!
2.10 Because your senses are your only tools for measuring the truth, consider what would happen if you constructed a house with a crooked ruler – if your square edge were bent and swerved from a straight line – if your level was bent. Without accurate tools to provide reliable measurements, your house would surely be crooked, with walls leaning in all directions, and without strength or symmetry. Such a building would be fatally flawed – ruined by the erroneous measurements and decisions on which it was built. In the very same way, false philosophies and religions will tell you that their conclusions are based on their “reason,” on “logic,” and on “revelation,” but because they are instead built on falsehood rather than verifiable evidence from the senses, you can be sure that they are instead distorted and false.
2.11[iii] Nature endows men with only three faculties of sensation by which to gain evidence about the universe, and “reason” is not among them. The three faculties of sensation given by Nature are: (1) the “five senses,” (2) the “passions,” and (3) the “anticipations.” These three categories may be considered as the three legs of a stool or a tripod. The first leg of this stool, which we commonly refer to as “the five senses,” is comprised of the senses of sight, sound, touch, taste, and smell. The second leg, the “passions,” are what we commonly refer to as the sense of pleasure and pain. The third leg, referred to as “anticipations” or “preconceptions,” is less familiar to us today, but is also a sense. The sense of anticipations is a faculty with which men are born, which develops with age, and which allows us to recognize abstract relationships that could not otherwise be recognized. Anticipations in men are analogous to instincts in animals. Anticipations are not innate “ideas,” for just as no kitten is born with the innate knowledge of a mouse, no man is born with innate knowledge of a law court. But kittens grow into cats which recognize certain patterns of behavior as desirable, and children grow into men with the ability to perceive abstract relationships such as justice and friendship. Without the faculty of anticipations, men would be unable to recognize these relationships at all, and – failing to recognize them – men would be unable to judge whether instances of these relationships are pleasing or painful.
2.12[iv] These three faculties are neither capable of reasoning nor of receiving impressions from memory. They do not themselves initiate any sensation on their own, and when they receive an impression from an external cause, they neither add to nor subtract from it. They are out of the reach of any control from one another, for one impression cannot judge another impression. It is in this way and for this reason that we hold that all sensations have equal value. Nor can one faculty judge another faculty, since the capacities of each faculty are not the same.
2.13 In other words, one impression cannot be judged to overrule another, since the effects of all impressions influence us equally. Here again we see that there is no separate faculty of “reason” that can independently pronounce judgment on a particular sensation. True reasoning is a process of forming conclusions based on opinions based on multiple sensations, and only based on other sensations can reasoning judge between alternative opinions. Even then, all sensations have been reported faithfully – it is the conclusion that is adjusted, not the sensation.
2.14 And in this process we must remember that the impressions of pain and pleasure, and the impressions from the anticipations, are just as real, and just as evident, as impressions of sight or hearing. All conclusions in which we may have confidence must be grounded in sensations received by any or all of our faculties, and it is only false philosophers who fail to acknowledge, and give proper weight, to sensations of pain and pleasure and sensations received through the anticipations.
2.15 We should prepare ourselves to encounter two situations frequently: (1) those situations where the evidence is direct and clear, and thus so evident that we grasp the truth of a matter immediately, and (2) those situations where the evidence is distorted, indirect, or otherwise unclear. In this latter situation, we must wait before we form a conclusion as to the truth of a matter. We must suspend judgment and seek truth through a process of “true reason,” by comparing – through analogy, proportion, or combination – new evidence that is not yet clear, and the tentative opinions that arise from them, against old evidence that has been established with clarity, and the certain conclusions we have reached previously based on that evidence.
2.16 It is by the process of evaluating the evidence of the senses that the mind forms conceptions of those things which are true. These conceptions are then applied to the evaluation of new matters. For example, the mind forms the conception of the idea of a “man” as being of such and such a nature. At the same moment that we consider the word “man,” we conceive the mental figure of a man because of the preceding operations of our senses. In fact, we could not judge the truth of any matter if we had not previously observed some example of that matter. In order for us to affirm that which we see at a distance is a horse or an ox, we must have a prior conception in our minds of the form of a horse and an ox. We could not even give names to things if we had not previously experienced some example of what the thing is. Thus our ability to be certain in reaching a new judgment depends on our ability to refer each new question to some previous judgment that we have found to be true. Confidence in our certainty of the prior judgment is the necessary foundation for affirming that a new judgment is true.
2.17 True reasoning requires that we firmly separate in our minds whether a matter is “true” or “false” or only an “opinion” or “supposition.” Matters of opinion or supposition must be clearly deemed to be neither true nor false, but only possible, until such time as sufficient evidence has been accumulated to reach a firm judgment. Those opinions which we find to be supported by sufficient evidence, and which are not contradicted by other evidence, are to be judged as true. Those opinions which are not supported by any evidence, and are in fact contradicted by evidence, are to be judged to be false. We must never consider opinions which are merely speculative to be entitled to equal weight in our minds as those opinions which are true, for if we do all our thoughts will be thrown into confusion.
2.18 As we will learn in physics, all that exists is matter constantly moving through void. We must therefore prepare our minds to accept that the forms and combinations of the elements are constantly changing. Yet even while movement and recombination of the elements occurs on and on without end, the nature of the elements themselves remains constant. Because the elements are eternal and unchanging, they possess unchanging qualities which provide limits and boundaries in the manner in which they move and combine. It is within the capacity of man’s senses – it is a requirement of man’s life – that we make judgments about the truth of particular matters at particular times and places.
2.19 Although there is no mystical trigger that allows us to reason to conclusions that will apply at all times and all places, there are principles of Nature (twelve of which are listed in the following section on Physics) that can be counted on as always true, and which provide a basis for seeking out truth in particular contexts. To hold that mystical concepts of virtue exist, and that these apply at all times and all places is the profound error of Platonic rationalism and idealism. The opposite mistake – the conclusion that the movement of the atoms prevents us from determining anything at all to be true – is the error of skepticism, and likewise of those who hold that “the only thing I know is that I know nothing.” The truth is that Life itself requires us to judge constantly to separate the true from the false and from the uncertain.
2.20 Our task is thus to consider the evidence available to us, and reach conclusions that embrace the essential concepts of the matter under consideration. We must grasp the essential concepts of a matter before we can perceive the whole of that matter, and before we can then understand how the particular aspects of the matter relate to the whole. In order for our judgment to be considered true, we must embrace in our mind a synthesis of the whole which accurately comprises within it the entire scope of that matter. Such a synthesis must encompass in a few words all the particular facts which have been established by the senses.
2.21 The process we are describing is essentially the same as “outlining” a matter as a means of assisting us in grasping its truth. Each essential concept should be formed into a concise statement, on which we then build a synthesis of all that we have succeeded in grasping. This method of observing Nature, by grasping essentials and then outlining the essentials so as to grasp the whole firmly, is a method that we should practice and pursue throughout our lives. It is this method of searching for truth which contributes more than anything else to the peacefulness and happiness of life.
2.22 As we pursue our outlines of understanding, we must first determine with exactness the meaning of – the concept which is comprehended under – each word that we employ. Each step along the way, we must be able to refer back to each concept as a certain standard on which to build further. It is to these conceptions, which we must build for ourselves, to which we must refer back as we examine each new matter and question – otherwise our judgments will have no foundation. Unless we build our understanding on firm concepts which we have clearly grasped, with each new concept built in turn on earlier firmly-grasped concepts, we gain nothing but mere words. It is thus absolutely necessary that we perceive directly and without reliance on anyone else the fundamental concept which each word expresses. This personal grasp is necessary if we wish to have any foundation on which we can verify our researches and judgments about the nature of things.
2.23 In order to judge that our perceptions are clear, we must observe carefully the impressions which we receive when we are in the closest presence of the matter under consideration. Those perceptions, which are obtained when the matter is grasped at close range and in greatest clarity, must be used as a standard to identify that point in any examination where we must reserve further judgment about to the truth of a matter. It is at this point – the point where we identify our perceptions as being insufficient or imprecise enough to form a clear judgment – that we must acknowledge that we do not have a clear determination of the matter. Only if we first lay a proper foundation, by grasping those things which are within our range of clear perception, are we ready to pass on to the study of those things about which the evidence is not clear.
2.24[v] As we proceed we must keep in mind the possibility of error and false judgment. Error arises when we suppose that a preconceived idea will be confirmed (or will not be overturned) by additional evidence as we receive it. In those cases where additional evidence does not confirm our supposition, we can look back and see that we have formed that supposition by connecting the evidence to a prior conception without sufficient information to do so. The point to remember is that the perceptions themselves did not deceive us, for the impressions we receive through our faculties are reflected from the matters under observation as if by a mirror. But the impressions we receive cannot be deemed to be real and true to the object we are observing unless we are examining those objects directly. When we err, it is because we do not properly recognize that our intelligence has connected these impressions with conceptions that go beyond what we have directly observed. It is not the senses that have failed, but our reasoning, and this is why we can never hold to be certain a theory of reasoning beyond that which the evidence supports.
2.25 We must carefully maintain these Canonical principles in our minds at all times so that we will never be tempted to reject the authority of our faculties. These faculties – given us by Nature – are our only means of discovering truth and living happily.
Many are the other marvels of this sort we see, which all seek to shake as it were the credit of the senses: quite in vain, since the greatest part of these cases cheats us on account of the mental suppositions which we add of ourselves, taking those things as seen which have not been seen by the senses. For nothing is harder than to separate manifest facts from doubtful which straightway the mind adds on of itself. Again if a man believe that nothing is known, he knows not whether this even can be known, since he admits he knows nothing. I will therefore decline to argue the case against him who places himself with head where his feet should be. And yet granting that he knows this, I would still put this question, since he has never yet seen any truth in things, whence he knows what knowing and not knowing severally are, and what it is that has produced the knowledge of the true and the false and what has proved the doubtful to differ from the certain. You will find that from the senses first has proceeded the knowledge of the true and the false and that the senses cannot be refuted. For that which is of itself to be able to refute things false by true things must from the nature of the case be proved to have the higher certainty. Well then, what must fairly be accounted of higher certainty than sense? Shall reason founded on false sense be able to contradict them, wholly founded as it is on the senses? And if they are not true, then all reason as well is rendered false. Or shall the ears be able to take the eyes to task, or the touch the ears? Again shall the taste call in question this touch, or the nostrils refute or the eyes controvert it? Not so, I guess; for each apart has its own distinct office, each its own power; and therefore we must perceive what is soft and cold or hot by one distinct faculty, by another perceive the different colors of things and thus see all objects which are conjoined with color. Taste too has its faculty apart; smells spring from one source, sounds from another. It must follow therefore that any one sense cannot confute any other. No nor can any sense take itself to task, since equal credit must be assigned to it at all times. What therefore has at any time appeared true to each sense, is true. And if reason shall be unable to explain away the cause why things which close at hand were square, at a distance looked round, it yet is better, if you are at a loss for the reason, to state erroneously the causes of each shape than to let slip from your grasp on any side things manifest and ruin the groundwork of belief and wrench up all the foundations on which rest life and existence. For not only would all reason give way, life itself would at once fall to the ground, unless you choose to trust the senses and shun precipices and all things else of this sort that are to be avoided, and to pursue the opposite things. All that host of words then be sure is quite unmeaning which has been drawn out in array against the senses. Once more, as in a building, if the rule first applied is wry, and the square is untrue and swerves from its straight lines, and if there is the slightest hitch in any part of the level, all the construction must be faulty, all must be wry, crooked, sloping, leaning forwards, leaning backwards, without symmetry, so that some parts seem ready to fall, others do fall, ruined all by the first erroneous measurements; so too all reason of things must needs prove to you distorted and false, which is founded on false senses.
[iii] From Diogenes Laertius Lives and Opinions of Eminent Philosophers, Book X: Now he divides philosophy into three parts. The canonical, the physical, and the ethical. The canonical, which serves as an introduction to knowledge, is contained in the single treatise which is called the Canon. The physical embraces the whole range of speculation on subjects of natural philosophy, and is contained in the thirty-seven books on Nature, and in the letters again it is discussed in an elementary manner. The ethical contains the discussions of Choice and Avoidance; and is comprised in the books about lives, and in some of the Letters, and in the treatise of the Chief Good. Accordingly, most people are in the habit of combining the canonical divisions with the physical; and then they designate the whole under the names of the criterion of the truth, and a discussion of principles, and elements. And they say that the physical division is concerned with production, and destruction, and Nature; and that the ethical division has reference to the objects of choice and avoidance, and lives, and the chief good of mankind.
Dialectics they wholly reject as superfluous. For they say that the correspondence of words with things is sufficient for the natural philosopher to enable him to advance with certainty in the study of Nature.
Now, in the Canon, Epicurus says that the criteria of truth are the senses, and the preconceptions, and the passions. But the Epicureans, in general, add also the perceptive impressions of the intellect. And he says the same thing in his Abridgment, which he addresses to Herodotus, and also in his Fundamental Principles. For, says he, the senses are devoid of reason, nor are they capable of receiving any impressions of memory. For they are not by themselves the cause of any motion, and when they have received any impression from any external cause, then they can add nothing to it, nor can they subtract anything from it. Moreover, they are out of the reach of any control; for one sensation cannot judge of another which resembles itself; for they have all an equal value. Nor can one judge of another which is different from itself; since their objects are not identical. In other words, one sensation cannot control another, since the effects of all of them influence us equally. Again, Reason cannot pronounce on the senses; for we have already said that all reasoning has the senses for its foundation. Reality and the evidence of sensation establish the certainty of the senses; for the impressions of sight and hearing are just as real, just as evident, as pain.
It follows from these considerations that we ought to judge of things which are obscure by their analogy to those which we perceive directly. In fact, every notion proceeds from the senses, either directly, or in consequence of some analogy, or proportion, or combination, reasoning having always a share in these last operations. The visions of insanity and of sleep have a real object for they act upon us; and that which has no reality can produce no action.
By preconception, the Epicureans meant a sort of comprehension as it were, or right opinion, or notion, or general idea which exists in us; or, in other words, the recollection of an external object often perceived beforehand. Such for instance, is the idea: “Man is being of such and such Nature.” At the same moment that we utter the word man, we conceive the figure of a man, in virtue of a preconception which we owe to the preceding operations of the senses. Therefore, the first notion which each word awakens in us is a correct one. In fact, we could not seek for anything if we had not previously some notion of it. To enable us to affirm that what we see at a distance is a horse or an ox, we must have some preconception in our minds which makes us acquainted with the form of a horse and an ox. We could not give names to things, if we had not preliminary notion of what the things were.
These preconceptions then furnish us with certainty. And with respect to judgments, their certainty depends on our referring them to some previous notion, of itself certain, in virtue of which we affirm such and such a judgment; for instance, “How do we know whether this thing is a man?”
The Epicureans also refer to ‘opinion’ as supposition, and say that it is at times true, and at times false. For that which is supported by evidence and not contradicted by evidence is true; but if it is not supported by evidence, and is contradicted by evidence, then it is false. On which account they have introduced the expression of “waiting,” as when, before pronouncing that a thing seen is a tower, we must wait till we come near, and learn what it looks like when we are near it.
They say that there are two passions, pleasure and pain, which affect everything alive. And that the one is natural, and the other foreign to our Nature; with reference to which all objects of choice and avoidance are judged of. They say also, that there are two kinds of investigation; the one about facts, the other about mere words. And this is as far as an elementary sketch can go – their doctrine about division, and about the criterion.
[iv] See Also: Sextus Empiricus Against the Logicians (translated by Richard Bett)
 What fools some people is the difference in the appearances that seem to strike us from the same perceptible (e.g., visible) thing, in virtue of which the existing thing appears to be of varying color or varying shape or in some other way changed. For they supposed that, of the appearances that thus differ and compete, one of them must be true, while the other one of opposite origins turns out to be false. Which is silly, and typical of men who fail to see the nature of reality.
For (to give the argument in the case of visible things) it is not the whole solid body that is seen, but the color of the solid body. And of color, some is on the solid body itself, as in the case of things looked at close up or from a moderate distance, while some is outside the solid body, and exists in the neighboring locations, as in the case of things observed from a great distance. But this changes in the space in between, and takes on its own shape, and hence gives off an appearance of the same kind as it is itself in its true existence.
 It is not the sound in the bronze instrument being struck that is heard, nor the sound in the mouth of the person yelling, but the one that strikes our sense; and no one says that the person who hears a faint sound from a distance hears it falsely given that on coming close he apprehends it as louder. Likewise, then, I would not say that one’s eyesight tells a falsehood because from a great distance one sees the tower as small and round, but from close up as larger and square, but rather that it tells the truth.
 Because when the perceptible thing appears to it small and of a such a shape, it is in fact small and of such a shape, since the edges of the images are broken off by their movement through the air; and when, by contrast, it appears large and of a different shape, it is, by contrast, equally large and of a different shape. However, it is not any longer the same thing that has both sets of features. For this is left to distorted opinion to think – that the thing that appears when observed close up and the thing that appears when observed from far away were the same thing.
 The specific role of sense-perception is to apprehend only the thing that is present and affecting it (for example, color), not to judge that the existing thing here and the existing thing there are distinct. Hence for these reasons all appearances are true, but opinions are not all true but have a certain diversity. For of these some are true and others are false, seeing that they are judgments of ours applied to the appearances, and we judge in some cases correctly, and in other cases badly – either as a result of adding something and assigning it to the appearances or as a result of taking something away from them and, in general, falsifying the non-rational sense-perception.
 Of opinions, then, according to Epicurus, some are true and some are false. The true ones are those that are testified in favor of, and not testified against, by plain experience, while false ones are those that are testified against and not testified in favor of by plain experience.
 “Testimony in favor” is an apprehension through plain experience of the fact that the thing on which the opinion is held is such as the opinion held it to be. For example, when Plato is approaching from a long way away, I conjecture and hold the opinion (given the distance) that it is Plato, but when he comes near there is additional testimony that it is Plato, now that the distance has been shortened, and there is testimony in favor of it through plain experience itself.
 “Absence of testimony against” is consistency of the unclear thing on which the supposition or opinion was held with what appears. For example, when Epicurus says that there is void, which is unclear, he confirms this through a matter that is plain, namely motion. For if there is not void there should not be motion, since the moving body does not have a place into which it can progress, on account of everything being full and solid –
 so that what appears does not testify against the unclear thing on which the opinion was held, since there is motion. “Testimony against,” however, is something that conflicts with “absence of testimony against.” For it is the exclusion, by the supposed unclear thing, of what appears. For example, the Stoic says that there is not void, maintaining something unclear. But when that is what has been supposed about this, the thing that appears (I mean motion) ought to be excluded along with it; for if there is not void, necessarily motion does not happen either, according to the method that we showed before.
 “Absence of testimony in favor” is also opposed in the same way to “testimony in favor.” For it is the impact through plain experience of the fact that the thing on which the opinion is held is not such as the opinion held it to be. For example, when someone is approaching from far away we conjecture (given the distance) that it is Plato, but when the distance has been shortened we get to know through plain experience that it is not Plato. And absence of testimony in favor is like this; for the thing that was opined was not testified for by what appeared.
 Hence testimony in favor and absence of testimony against are the criterion of something’s being true, while absence of testimony in favor and testimony against are the criterion of something’s being false. But the grounding and foundation of all of them is plain experience.
[v] Letter to Herodotus – This leads us to observe the possibility of error and false judgments, which always depend upon our supposing that a preconceived idea will be confirmed, or at any event will not be overturned, by additional evidence as we receive it. In those cases where our supposition is not confirmed, we form our judgments in virtue of a sort of initiation of thought which is connected with our perceptions, and with a direct representation from the object that we observe. In these cases of error, however, the connection is with a conception that is peculiar to ourselves, and this is the parent of error. In fact, the representations we receive from images are reflected by our intelligence like a mirror, whether those images are perceived in a dream or through any other conceptions of the mind or the senses. But these representations do not resemble the objects to the extent that we can call them real and true unless the objects that we are examining are perceived directly. Error arises when we do not perceive objects directly because in those situations we receive impressions which our intelligence connects with a direct representation, but which goes beyond a direct observation. These conceptions are connected with direct perception which produced the representation, but they go beyond the actual object in consequence of impressions that are peculiar to the individual making them. This results in error when the mental apprehension our minds reach is not confirmed by, or is contradicted by, additional evidence. When our mental apprehension is confirmed by additional evidence, or when it is not contradicted by additional evidence, then it produces truth. We must carefully preserve these principles in order that we will not reject the authority of those of our faculties which perceive truth directly. We must also observe these principles so that we will not allow our minds to believe that what is false or what is speculative has been established with equal firmness with what is true, because this results in everything being thrown into confusion.