Are There Truths We Cannot Not-Know

Hey guys, this is another paper I had to do for school, do enjoy, do not copy.

In the Eighth Book of his Metaphysics, Aristotle proceeds to argue against the theory of perception, a theory that is held by some of the Pre-Socratics, namely Heraclitus and Anaxagoras, and by the later sophist Protagoras. The theory of perception dictates that the perceptions of any person are in all cases true, hence the idea in Protagoras that man is the measure of all things, i.e. viz. himself. Of course, this theory necessarily requires that the whole Universe be in constant flux, because if there were any principles that were constant, they would be true at all times regardless of whether someone perceived them as such or not. In the end, the theory of perception seeks to end any claim made about objective truth and turns the nature of all reality toward the singular perception of any individual.

Aristotle, perhaps unsurprisingly, rejects this view in its totality. He mounts five basic reasons why this theory cannot be true and is, in fact, nonsensical. In addition to these five points, it is obvious from the text that if such theory were true, it would be necessary that every person would know it from birth, because it could be readily perceived as such. In itself, that is a contradiction, because, as Aristotle points out, “if all are false it will not be true that all are false, and if all are true it will not be false to say all are false.”[1] That is to say, that if this view were true, then to point out that this view is true would be the same thing as pointing out that this view is false. In making his arguments, Aristotle borrows heavily from Plato, specifically the Theatetus, where Plato, in the person of Socrates, mounts his own attack against the theory of perception. Of course, Aristotle restates some of the valid reasons that Plato has already formulated and, in a few cases, points out new implications of them and furthers Plato’s claims.

The first argument that Aristotle makes against the theory of perception is the idea that language in itself relies on the unchanging Principle of Non-Contradiction in order to function. That is to say, that one can safely assume that when they speak the word “dog,” the person to whom the word is spoken to will understand that he is speaking about “dog” and not “non-dog,” i.e. that a word cannot mean “dog” and “non-dog” at the same time and in the same respect. Without this tacit agreement between conversation partners, no communication of any sort that relies on language is possible. As Aristotle points out, “It would seem also that in saying the man is not a horse we should be either more or not less right than in saying he is not a man, so that we shall be right in saying that the same person is a horse; for it was assumed to be possible to make opposite statements equally truly.”[2] It is quite obvious that language cannot function in this environment.

This is an argument that Plato makes in the Theatetus. Aristotle goes on to point out, as does Plato, that, on these terms one cannot have a reasoned discussion with anyone, “[t]erefore, with these men there is no reasoning. But as for those who are perplexed by the traditional difficulties, it is easy to meet them and to dissipate the caused of their perplexity.”[3] Aristotle points out here that whereas, if someone were to seek refutation of the theory of perception, they could be given logical reasons against it, they could not be given logical reasons for it, because the theory of perception, seeking to deny the Principle of Non-Contradiction, is inherently illogical.

The second point, which is also shared with Plato’s Theatetus, is that the theory of perception is self-contradictory. Aristotle points out that since the affirmation of a thing is equally true to its negation, then one cannot conclusively affirm or deny anything. Aristotle is quick to point out that, “… if it is not possible to affirm anything truly, this itself [i.e. the theory of perception] will be false—the assertion is that there is no true affirmation. But if a true affirmation exists [i.e. that the theory of perception is true], this appears to refute what is said by those who raise such objections…”[4] The scenario is, basically, that if there is no true affirmations, then the theory of perception is not necessarily true, and, if the theory of perception is to he held as true, its own content contradicts with it.

This points out that, under its very own precepts, it is self-contradictory to teach the theory of perception. To teach such a theory, if it were true, would be equivalent to teaching exactly how I cold or warm I felt at 12:31 PM today. Though, granted, I could presume to tell someone whether I felt warm or cold at 12:31 PM today, the information would be of no use to him or me, but teaching presupposes that the information relayed will be of some use to the students. Therefore, if it were illogical to teach it, the only recourse for the theory of perception to be true would be for every person to know it independently, but because this is not the case, it cannot be true.[5]

The third point that Aristotle makes is the idea that the theory of perception is an exaggeration of a true principle in a limited amount of cases, i.e. subjective sensations. In this, he drives further than Plato, who says that the theory of perception is true in cases of subjective sensation. Aristotle points out that even though the sensations of different people may be different, they only vary in degree (some people may find whipped cream more sweet than others), but that there are no two people who would, respectively, get two different sensations from the same thing, i.e. there are no two people that would find whipped cream respectively sweet and bitter. If such a case arises, then one of the two people must have some damage in the sensory organ. This is true for cases such as light hypersensitivity, where the sensate organ of sight is damaged in people who find a normal amount of light painful.[6]

In fact, Aristotle points out that even the same person can have two contradictory sensations of the same thing, when they are sick as opposed to when they are healthy, but there has been a qualitative change in the sensor rather than in the object sensed that has changed the sensation.[7] The point is that these contradictory sensations are neither at the same time, nor in the same respect, since the person sensing has changed. In saying this, Aristotle goes back to Plato in saying that, regardless of the differences in sensation among different sensors, the thing sensed is consistent in itself, in that whipped cream has not suddenly become bitter as opposed to sweet when a man who was previously healthy tasted it when he was sick and back to sweet when he regained his health.

Aristotle next points out that it is illogical to think that because things that are of a certain quality can be changed into being another thing they are both things at the same time. He points out that, if a thing is changed into another, “it follows that that which is moved must first be in that out of which it is to be moved and then not be in it, and move into the other and come to be in it…”[8] That is to say that, in order for a thing to change, it must first be actually be part of group “x” and potentially part of group “y”, but it is not necessary or true that it must be in both groups at the same time, otherwise there would be no change. Flux presupposes this distinction.

He continues to point out that, for the theory of perception to be true, all matter must, necessarily, change both qualitatively and quantitatively constantly. Aristotle argues that, even though one could, from faulty observation, suppose that everything changes quantitatively constantly, things do not change constantly qualitatively, therefore, the theory of perception falls again.

Lastly, Aristotle points, as Plato, that, in times of emergency, people seek out experts in each field, thereby affirming that there are degrees of wisdom. Sick people seek out a doctor and proceed to follow what they prescribe them, which would be illogical if every person had all knowledge available to them. In addition, they follow the doctor’s orders; they eat bread if the doctor tells them to eat bread and do not argue about why that which is prescribed is bread as opposed to non-bread.[9] Of course, if the theory of perception were true, “they should not, if there were not fixed constant nature in sensible things, but all moved and flowered for ever.”[10]

It is interesting to point out that one of the implications of this refutation of the theory of perception and, frankly, something that is taken as self-evident in this argument is the fact that there are certain truth-claims that everyone knows instinctually. That is to say, that there is such a thing as common sense. In this, it seems that Aristotle anticipates and provides a contradiction for Renee Descartes’ claim that one can only know for sure those things which to doubt would be illogical. The implication of that view is that only people formally engaged in logic could truly know things and that, by necessity, common sense would have to be dismissed.

Ralf McInerny resolves to point out the arguments in Aristotle and St. Thomas Aquinas prove that, by necessity, everyone must have access to certain truth claims. McInerny’s first point is that the fact that humans possess language points out that they have a basic understanding of the Principle of Non-Contradiction. He says, “If it is true that the bike is now in the garage, it cannot be true that it is not in the garage. If it is true that you promised something, it cannot be true that you did not.”[11] In truth, every human can testify to the tacit agreement of this principle in every case of this sort. The fact that humans argue at all, in fact, is proof of the idea that there must be an implicit agreement of the principle behind it[12], otherwise people, like animals, would simply fight.

Since every human has reason, every human must possess the knowledge of the Principle of Non-Contradiction, otherwise reason would be impossible. McInerny points out that our very ability to deny the Principle of Non-Contradiction proves that it must exist[13], because if it did not exist, as Aristotle points out in his first argument against the theory of perception, its affirmation and negation would have equal truth value and would be both equally devoid of value.

McInerny then deals with the criticism that innate ideas are, in one way or another, useless, because they do not point out anything about reality. Of course, this is simply not true. The Principle of Non-Contradiction may not make any distinction about kinds of things, etc., but it makes a distinction in all things, specifically that they cannot be and not be at the same time and in the same respect.[14] By the same logic, the saying “do good and avoid evil” does not make any distinction about how to do good and avoid evil, but it does point out that good is not evil and that evil is not good, i.e. that they are distinct from one another.[15] In both cases, however, as Aristotle has pointed out, it is necessary that the idea of the principle remain constant throughout for it to make any sense at all and, if this is true, the idea is either objectively true or objectively false, regardless of what one may perceive about them. McInerny develops Aristotle’s points further here, in saying that since the Principle of Non-Contradiction is innate to all people, the tools to argue against the theory of perception are present to all people.

In addition, because these principles aid and facilitate thinking rather than being “pre-stored” information, they are outwardly exhibited first in specific cases, i.e. “the bike cannot be in and out of the garage at the same time”, or “it is good to help others,” and the formal statement of the principle comes later in someone’s life[16], concerning the inward person, it is the principle that pre-exists the application of it into specific cases, albeit subconsciously, so that the general principle must have existed first in order to have gotten specific applications of it. This is supported and presupposed in the argument against the theory of perception, because without the pre-existence of the Principle of Non-Contradiction language could not exist and people would not be able to not only communicate with each other, but use anyone else’s language system.

McInerny also points out that there are instincts in the human that are assumed to be good, such as “that I should preserve myself in existence, avoiding dangers to life and fending off attacks, and that I should eat and drink to preserve my life.”[17] Of course, if the theory of perception were true, one could not term these instincts as either “good” or “bad. In addition, since to eat and not to eat would be equivalent to one another, people who could not make that rational distinction would starve themselves, which would bring the unequal effect of their death (that is as opposed to eating). Because most people, when they reach the time of rationality, do not starve themselves, it would seem that the Principle of Non-Contradiction has already exhibited itself in them.

All in all, Aristotle’s attack against the theory of perception wins out in all points. It seems that just about anything that could possibly go wrong with an argument goes wrong with that argument. Of equal importance, it is a necessary implication of the refutation of the theory of perception that everyone must have certain innate ideas in them, through which they are able to function in society. It is important to note that if this claim were not true, i.e. that all people have access and truly know the Principle of Non-Contradiction, the theory of perception would gain much strength, but, on the other hand, there is undeniable evidence to the contrary, i.e. that humans communicate, discuss, and argue with each other, a behavior which is not seen in the animal kingdom, where the default means to solve conflict is physical confrontation. The very fact that we are able to discriminate amongst our instincts between “good” and “bad” shows that the Principle of Non-Contradiction is well in place. In addition, the fact that choosing one contrary over another brings forth very different effects is the last nail on the coffin of theory of perception and points out that it is necessary that every person have access to basic logic.

Works Cited

Aristotle. The Complete Works of Aristotle: The Revised Oxford Translation. Trans. Jonathan Barnes. Vol. 2. Princeton, NJ: Princeton UP, 1995. Print.

McInerny, Ralph.  “Are There Moral Truths that Everyone Knows?” in E. McLean (Ed.),  Common Truths. (Wilmington: Intercollegiate Studies Institute Books, 1999), pp. 1-15.


[1] Aristotle, Metaphysics. Book VIII. 6, 1063b34-5=pg. 1680

[2] Aristotle, Metaphysics. Book VIII. 5, 1062a25-8=pg. 1678

[3] Aristotle, Metaphysics. Book VIII. 6, 1063b11-4=pg. 1680

[4] Aristotle, Metaphysics. Book VIII. 5, 1062b 6-11=pg. 1678

[5] Refer to the point made before the examination of Aristotle’s arguments about how, even if everyone knew the theory of perception independently, it would still make it invalid.

[6] Aristotle, Metaphysics. Book VIII. 6 1063a1-4=pg. 1679

[7] Aristotle, Metaphysics. Book VIII. 6 1063B1-6=pg. 1680

[8] Aristotle, Metaphysics. Book VIII. 6 1063a19-23=pg. 1679

[9] Aristotle, Metaphysics. Book VIII. 6 1063b29-32

[10] Aristotle, Metaphysics. Book VIII. 6 1063b32-34

[11] McInerny, Ralph. Common Truths, “Are there Moral Truths That Everyone Knows?” pg. 9

[12] McInerny, Ralph. Common Truths, “Are there Moral Truths That Everyone Knows?” pg. 9

[13] McInerny, Ralph. Common Truths, “Are there Moral Truths That Everyone Knows?” pg. 7

[14] McInerny, Ralph. Common Truths, “Are there Moral Truths That Everyone Knows?” pg. 8

[15] McInerny, Ralph. Common Truths, “Are there Moral Truths That Everyone Knows?” pg. 11

[16] McInerny, Ralph. Common Truths, “Are there Moral Truths That Everyone Knows?” pg. 14

[17] McInerny, Ralph. Common Truths, “Are there Moral Truths That Everyone Knows?” pg. 13

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