Epistemology: The Problem of Perception

Perception the Epistemological Starting Point:  A Study of Locke’s, Berkeley’s and Aristotle’s Epistemological Approach to the Question of Perception and the Nature of Reality

By, Carl Waidell

In the study of Epistemology, there is the understanding that a philosopher’s position on the notion of perception and reality are pivotal when considering how one should view immediate objects. Within the field of the “Philosophy of Knowledge” there are many different starting points all of which will lead in a determinate view of one’s perception of reality. This conflict of opposing views is not a new one; it can be traced back to Socrates, Plato, and Aristotle to name the most popular.  Still, in the age of modernity, the challenge remains, how is one to view reality? It is argued that if one's starting point for epistemology is wrong that it will lead to a labyrinth of problems needing answers to work its way back to stable ground.  Indeed, this is the sentiment of many when approaching the “Epistemological Subjectivist” or the “Idealist.”  Subjectivism is the philosophy of knowledge that finds a starting point in the subject, the “I” or the “private ego,” and tries to determine how one should approach material matter; it is from the “inside out” so to speak. On the other side of the argument is the “Epistemological Realist” who holds the view that one’s consciousness immediately puts them in contact with the other.  It is the idea that because a person is a rational conscious being and, as such, can interact with that which is “the other” as sensory objects.  

  In light of this argument, the questions needing answering are: what is the difference between the opposing positions and why is it essential in the study of epistemology? This project will look at three different epistemological views, those of John Locke, George Berkeley, and Aristotle. This report will look at their specific views on the matter, determine the strengths and weakness of their arguments, and apply logical rationale as to the outcome of all of their positions on the Philosophy of Knowledge.

John Locke’s Representationism: The image theory of perception

John Locke is classified as an “empiricist," and much like Descartes, he had a passion for clear and distinct ideas and thereby sought to establish a stable foundation for the perception of reality. Locke’s epistemology is best known as representationism which The Oxford Dictionary defines as: “The doctrine that thought is the manipulation of mental representations which correspond to external states or objects.[1] He believed that all knowledge is attained through sense-data and therefore our ideas are only representations of reality.

            However, understanding what Locke means by “ideas” is critical for comprehending his epistemology.  With logic, if one does not have clear and unambiguous terms, it is impossible to determine the truth-value of any argument, and Locke states his terms clearly.  First, all knowledge is attained through the senses or sense-data.  This data is important to our understanding of reason because, unlike Plato, he believed that man was not born with innate ideas, and therefore, the mind is a blank slate at birth. Locke’s gateway to understanding is one’s comprehension of his theory of “simple, complex, and mixed modes” as discussed in his work, An Essay Concerning Human Understanding.

            Simple modes are singular particulars that will eventually be used to construct complex modes or ideas. Simple modes are particular units of ideas which stand alone in comprehending reality.  It is the distinctness of what greenness is in grass or the thickness of its strands. They are one single unit or measurement of an external state or object.

“Those modifications of any one simple idea (which, as has been said, I call simple modes) are as perfectly different and distinct ideas in the mind as those of the greatest distance or contrariety.”[2]

These simple modes, according to Locke, are constructs of a passive mind that receives them from sense experience and the operation of things, like sensations or reflections.[3]  Putting it another way, our mind is a passive consciousness that reflects what can be known about an object. Ideas are forced on us by the use of our sense perceptions and sense-data.

            Complex modes are the joining together of simple modes whereby, the mind becomes active in constructing combinations of simple ideas into a unified complex idea or ideas of external states or objects. Complex and mixed modes are similar to, but not consistent with, Aristotle’s idea of working from particulars to understand the universal thing as a sort-of-a-whole. However, Locke seems to hold on to a pseudo-nominalist construct that implies that all complex ideas are only brought under a universal banner in order to describe the multiple simple ideas.  It is a sort of extensive understanding of the particulars described in one new term or idea. This is where his epistemology addresses the use of terms, symbols, and language.

Locke held the belief that language is that which combines multiple simple ideas into complex ones. Language joins several simple ideas under the banner of a new term and, as such, is accessible to comprehension by others. With that in mind, he also points out that there are several weaknesses with language since words may not mean the same things to every person. Because of this, he held that view that all words and ideas should be well defined and used consistently.

            Returning to Locke's simple and complex ideas leads him to a precarious position when dealing with his perception of reality.  The questions needing answering are: how can one know their ideas represent objective reality?  If ideas are subjective by nature, then how is it that one can get out of their mind and view reality as that which it is?

 In answering these questions, Locke introduces the idea of primary qualities and secondary qualities.  Primary qualities are those qualities that essentially belong to bodies, namely, solidly, extension, figure, motion, and rest.  These essential qualities reduce Locke's universe into a geometrical form.  Secondary qualities such as color, odor, or taste do not exist necessarily in the object and therefore have no real basis in our perception of reality.  For instance, a tomato may be known based on its primary qualities of shape and extension but it is redness is only known under right conditions and proper comprehension by sight, and therefore, are not conducive to anything but ideas concerning reality.

With that said, Locke still presents himself with some questions needing answering if one is to take his theory seriously.  The first is how does Locke know that his ideas are representative of tangible material objects? Secondly, his epistemology is similar to Descartes ideas of subjectivism how does one get out of their head in order to have a clear comprehension of material objects?  Lastly, how can Locke defend his position for the existence of primary qualities and the nonexistence of secondary qualities?  It is at this point that the philosopher George Berkeley arrives to address the issues.  

George Berkeley – A deeper understanding of Idealism

Berkeley is probably the one that contended with Locke’s notion of idealism more than any other philosopher.  It is not that Berkeley was not an idealist it was instead that he considered Locke’s, view of idealism as a “wrong notion” as to what true idealism was. Therefore, in his three “Dialogues between Hylas and Philonous” Berkeley wants to set the matter straight. 

            In the spirit of “setting the matter straight," one must ask: what does Berkeley's epistemological idealism entail?  Upon first reading his essays one could take his writings as nonsensical but with more in-depth understanding his ideas on the matter become more apparent.  His first point is that all existing things only exist in our minds. Secondly, there are not mind-independent existences out in the world. Thirdly, objects are nothing more but collections of ideas.

  With this as is an epistemological starting point, Berkeley wants to move past non-philosophical common sense ideas to deeper philosophical thinking on the matter. In his first dialogue Berkeley as pseudo-Philonous claims that he wanted to defend common sense and to persuade Hylas to see the common sense nature of his argument. His argument had four points that he wanted to convey. The first is that one can trust their senses.  What one knows immediately of objects are not illusions or distortions. Secondly, qualities we immediately perceive as existing in things do exist. This is one of the primary differences between Locke and Berkeley's idealism. Locke believes in the existence of primary qualities and discounted secondary qualities while Berkeley believed that neither one could be recognized to exist outside the mind. The third common sense point that he makes is that the things one sees and feels are real and not just representations of things but ideas in the mind. Berkeley does not deny conventional reality; he would concur that the car one drives is real, but that is not his point of contention. What he wanted to do is refute the skeptics and Locke’s wrong notion of idealism. His last position is that all skeptical doubt about the real existence of things is unjustified. With the argument outlined Berkeley wanted to convey five ideas concerning the problem of perception.

            Berkeley’s first point is that there is no reason to believe in the existence of mind-independent material objects. He takes exception to Locke's notion that there is a difference between primary and secondary qualities. He argues that when experiencing immediate objects, one does not recognize the substratum of primary qualities without sensing the secondary ones as well. It is his idea of esse est percipi. Alternatively, as Kenneth Gallagher explains, “…[H]is complete formula should read: ‘esse est aut percipere aut percipi’ – to be is either to perceive or be perceived; for he allows that there are two ways of being: as a mind or as the object of the mind. I exist, and the objects of my conscious experience exist (my ideas). But that is all I can mean by existence.”[4]

  Berkeley's second point is that we are not presented with any mind-independent material objects in our immediate experiences.  All knowledge comes through the senses; therefore, all one knows are ideas about primary and secondary qualities. In his pseudo-dialogue with Hylas, Philonous challenges him on the point that perception is not mind-independent and that nothing is perceived without the mind.

"… I am content to put the whole upon this issue. If you can conceive it possible for any mixture or combination of qualities, or any sensible object whatever, to exist without the mind, then I will grant it actually to be so."[5]

  His next item is that there is no such thing as mind-independent matter –because there is no evidence to support the notion.

“Once we see that matter, considered as an independent entity, is a ridiculous fiction, [then] all sorts of foolish problems are avoided, such as the worry over whether my ideas correspond to anything other than themselves; the reason is that there is not ‘external’ world independent of ideas for these ideas to ‘correspond to.’”[6]

His last argument is to establish the “Absolute Mind” whereby all things exist in a mind-dependent absolute.  It is this concept of Berkeley's that he uses to validate that all material objects exist because the absolute mind perceives them.

            Berkeley’s arguments are designed to challenge Locke’s idealism and show the logical conclusion of his line of reasoning.  The fact that Locke stopped with the nonexistence of secondary qualities only was a pivot whereby Berkeley could point idealism to its logical conclusion.  Berkeley was so to speak, "the finger pointing to the moon." However, the question remains: is the epistemological idealist's perception of how one should view reality valid?  Many would argue that it is.  However, what does the other side of the argument have to say concerning the problem with perception?  To this question, Aristotle is one of the most influential voices when addressing the nature of things.

Aristotle’s Epistemology

Aristotle’s epistemology in most respects is counter-intuitive to that of Locke's and Berkeley's.  He believed that there is no preexistence of the soul, and to understand reality is not the outcome of the recollection of preexistent knowledge. To the contrary, his idea, similar to Locke’s was that at birth we are like a blank slate without impression or knowledge.  All knowledge is learned through sensory perception that is an accumulation of previously conceived memories. Knowledge of forms is learned by beginning with an initial sensory experience of an object. In constant contact with this object one begins to develop a sort-of-a-whole, also called a universal. With constant contact and memories, a particular object can be understood by the universal knowledge of what it is. For instance, a child, as it grows in maturity, begins to recognize the form of a man because she has her first sensory perception of her father. Through recurring contact with him, she begins to know him as the form of a man distinctly different than her dog.  By his personality and his traits, she begins to understand him as a type of a species, that of man.  Eventually, she comprehends him in his particular relationship and his personality as her father. 

Aristotle's epistemology begins with sensory perception and matures with the ideas of categories and concepts. For Aristotle, a concept begins with categorizing and labeling things that are similar or dissimilar in a particular object.  In his book, Categories, Aristotle identifies ten different categories whereby a thing might be known.  However, the three most important categories are quality, quantity, and relation. To illustrate how categories and concept are achieved one starts with a substance and begins to ask questions to understand a particular substance. Through questioning a substance can be categorized and understood universally and as a particular sort-of-thing. For example, a teacher using Aristotle's method begins without the students' knowledge of what a particular object is. The students begin asking questions. Is it an animate object or an inanimate object?  The teacher replies, it is alive.  Another student asks, is it an animal or a plant?  It is an animal, she responds.  Does it have two legs or four? Four, she says to the students. Is it a dog? No. What type of nose does it have? A very long one.  Is it an elephant? Yes. The students reply, ok we have answered the questions, and we have arrived at the answer.  She replies yes and no.  You have answered what the species is but not the particular animal I have in mind.  With another round of questions, the class comes to the understanding of a particular elephant with the name of Tina, that lives in Las Vegas, and performs at shows nightly.

Aristotle like Plato wanted to view the universe with stable rather than relativistic ideas.  Aristotle taking a completely different approach to reality wanted to understand the whole-of- thing by examining that which can be known through the senses. As a dialectician, he saw reality as puzzles to be solved as stated in Nicomachean Ethics.

As in all the other cases, we must set out the appearances and first of all go through the puzzles. In this way, we must prove the common beliefs [endoxa] . . . ideally all the common beliefs, but if not all, then most of them and the most important. For if the problems are solved and the common beliefs are left, it will be an adequate proof.[7]

The definition of endoxa is common beliefs as described in his work, Tropics, writing, “[endoxa] The things believed by everyone or by most people or by the wise (and among the wise by all or most or by those most known and commonly recognized).”[8] Aristotle's approach to solving puzzles was the use of inductive and deductive methods of logic. Traditional beliefs in their unchallenged form can be unstable; they can be either true or false. The question is, how can we know which common beliefs are true or false in order to solve the puzzles presented to us. By employing the use of inductive (high probability, general, universal knowledge) and deductive (certainty, particular knowledge) logic, the puzzles could be solved and thereby, provide a degree of certainty that would be adequate proof of their truthfulness. An example of his dialectic approach is that which is exhibited by Thomas Aquinas in his work, On Law and Natural Law.  Aquinas in this essay discussed three types of law.  His initial starting point for this work is the “eternal law” (universal law). Once establishing eternal law, and what it is, he works toward its end by showing that human law has its basis and functions in the eternal law and is thereby of the same essence or genera and species of divine law. Working further Thomas shows that human law, a particular form of both natural law (species) and eternal law (genera) can be logically accepted as adequate proof of its truthfulness.

Aristotle's process is systematic utilizing inductive and deductive logic to arrive at a particular reality. The system starts with observations about phenomena, and through the induction, process questions are asked that lead to general principles which in turn lead to deductive logic to know, with some degree of certainty, what the phenomena being observed is. This process continues in a spiral working from observed objects to general principles to deductions eventually leading to particular knowledge of the phenomena observed. 

Returning to its epistemological problem with perception it is clear that Locke and Berkeley are on opposite sides of the issue.  Take for instance Idealism's view that external states or objects are nothing more than ideas in the mind. Aristotle, on the other hand, would disagree with them insisting that we are in immediate contact with objects and external states that do exist. 

In contrasting the two positions on the perception of reality, the idealist seems to have a few big problems to address before it can find itself on stable ground as mentioned above. These questions are: how do Locke and Berkeley know that their ideas are representative of tangible material objects?  How does one get out of their mind in order to have a clear comprehension of material objects?  Lastly, how can Locke and Berkeley defend their positions for the non-existence of qualities? If these questions cannot be answered definitively how is it that idealism can claim to have stable ideas concerning reality.

When looking to Aristotle's view, his philosophy answers these questions.  First, because a thing does materially exist, they can be known through the sense perception of particular things.  As a particular thing is studied there are qualities that can be said to exist in them which become universal knowledge of the thing studied.  Therefore, material things can be known. The things studied are not representations or copies they are immediately known through the senses. Because this is so, Aristotle has no problem with the first two questions asked of Locke and Berkeley. The last question: how can Locke and Berkeley defend their positions for the non-existence of qualities? Aristotle’s epistemology answers this question because in his theory of knowledge these primary and secondary qualities do exist. Dogs can be recognized as dogs through the understanding of genera and species and the addition of accidental qualities such as size or color.  

While examining these questions, it is evident that Aristotle is on a much more stable foundation.  His theory of knowledge does not have the same problem with perception that the idealists do.  It is here that one can see that the epistemological starting point has a significant impact on how one perceives reality.  For instance, the idealism of Locke and Berkeley places them in a world that does not have any existential import.  There are no tangible material objects that can be known.  The only thing that can be said is what was quoted earlier by Gallagher concerning Berkeley, “…[H]is complete formula should read: ‘esse est aut percipere aut percipi’ – to be is either to perceive or be perceived; for he allows that there are two ways of being: as a mind or as the object of the mind. I exist, and the objects of my conscious experience exist (my ideas). But that is all I can mean by existence.”[9] This quote's sums up what can be said concerning idealism all material things can only exist that in the mind as ideas - period.  

Aristotle, on the other hand, would contend otherwise. His epistemology puts one in direct contact with material objects.  They are known by employing inductive and deductive logic working form particulars to universals or a sort-of-a-whole.  With this universal knowledge, one is placed in direct contact with particular material objects.

In conclusion, this essay has looked at three different epistemological views, those of John Locke, George Berkeley, and Aristotle. It has looked at their specific views on the matter, determined the strengths and weakness of their arguments, and applied logical rationale as to the outcome of all of their positions on the “Philosophy of Knowledge.”


Berkeley, George. "The First Dialogue Between Hylas and Philonous." In A Modern Introduction to Philosophy: Readings from Classical and Contemporary Sources, edited by Paul Edwards, & Arthur Pape, 584-615. New York: The Free Press, 1973. This is Berkeley’s rebuttal to John Locke’s position concerning Idealism.  There are three dialogues in total.

Gallagher, Kenneth T. Philsophy of Knowledge. FB&C Ltd, Dalton House, 2018.

This is a text book on Epistemology.  It is comprehensive and highlights the arguments displayed in this paper.  However, the section on Aristotle in this writing is not addressed by Gallagher

Locke, John. "An Essay Concerning Human Understanding." In Modern Philosophy: An Anthology of Primary Sources, edited by Rodger Ariew, & Watkins Eric, 316-421. Indianapolis/Cambridge: Hackett Publishing Company Inc., 2009. This is Locke’s priar source for his “Epistemological Idealism” it is comprehensive and clearly written.

Miller, C.D.C. Reeve & Patrick Lee, ed. Introductory Readings in Ancient Greek and Roman Philosophy. Translated by C.D.C Reeve. Indianapolis: Hacket Publishing Company, Inc., 2006. This text book is a collection of primary sources.  This text was the primary one used to develop Aristotle’s ideas and epistemology.

Oxford University Press. "OxfordDictionaries." English Oxford Living Dictionaries. 2017. https://en.oxforddictionaries.com/definition/representationalism (accessed March 23, 2017).

The sources below we studied but not cited.

Aquinas, Thomas. Thomas Aquinas: Selected Writings. Edited by Ralph McInerny. Translated by Ralph McInerny. London: Penguin Books, 1998.

Berkeley, George. "A Treatise Concerning the Principles of Human Knowledge (1710)." In Modern Philsophy: An Anthology of Primary Sources, edited by Rodger Ariew, & Eric Watkins, 438-453. Indianapolis/Cambridge: Hackett Publishing Company Inc., 2009.

Locke, John. "Sense Qualities and Material Substances." In A Modern Introduction to Philosophy: Readings from Classical and Contemporary Sources, edited by Paul Edwards, & Arthur Pap, 577-583. New York: The Free Press, 1973.

McInery, Ralph, and O'Callahan John. "The Stanford Encyclopedia of Philosophy." Saint Thomas Aquinas. https://plato.stanford.edu/cgi-bin/encyclopedia/archinfo.cgi?entry=aquinas. Edited by Edward N. Zalta. Meta Physics Reasearch Lab, Stanford University, 2018.

Michael J. Dodds, O.P. The Philosophy of Nature. Oakland, CA: Western Dominican Province, 2010.

Pappas, George S. "Berkeley's Assessment of Locke's Epistemology." Philosophica 76. 2005. http://www.philosophica.ugent.be/fulltexts/76-5.pdf (accessed April 6, 2019).

The Ayn Rand Institute. "George Berkeley: From Empiricism to Idealism." The Ayn Rand Institute. n.d. https://campus.aynrand.org/campus/globals/transcripts/george-berkeley-from-empiricism-to-idealism (accessed April 5, 2019).


[1] English Oxford Living Dictionaries, “representationism,” 2017, https://en.oxforddictionaries.com/definition/representationalism (accessed April, 16, 2019).

[2] John Locke, “An Essay Concerning Human Understanding,” in Modern Philosophy: An Anthology of Primary Sources, ed. Roger Ariew and Eric Watkins, (Indianapolis/Cambridge: Hackett Publishing Company Inc., 2009),342.

[3]  (Locke, An Essay Concerning Human Understanding, 2009, 357)

[4] Kenneth Gallagher, Philosophy of Knowledge, (FB&C Ltd, Dalton House, 2018),


[5] Berkeley, George. "The First Dialogue Between Hylas and Philonous."

In A Modern Introduction to Philosophy: Readings from Classical and Contemporary Sources, edited by Paul Edwards,  & Arthur Pape, (New York: The Free Press, 1973), 608.

[6] (Gallagher, 2018, 79) Gallagher miss used the word than rather than then.

              [7] Patrick Lee and Reeve Miller, ed. and trans., Introductory Reading of Ancient Greek and Roman Philsophy, (Indianapolis: Hacket Publishing Company, Inc., 2006), 247.

[8] (Miller 2006, 258)  

[9]  (Gallagher 2018, 78)