Theory of Knowledge




21 June 2016

Theory of Knowledge


Quine postulated that necessary truth as being functional systems that encompass the concept of generality which are based on objective quantifiers (Lean 103). Quine’s perspectives revolve around the role of principle of identity in conferring and identifying truth. He strongly believed that quantified modallogic has significant uncertainties when analysed from the logical and philosophical perspectives (Lean 103). The theorist emphasizes on the fact that the principle of identity is derived from the principle of substitutivity (Lean 103). It is with this regards that the theorist considers that two different statements can be identified as being true provided that they can be substituted without changing the main variables and representative principles (Lean 103). This approach can be used to mitigate skepticism based on its referral capabilities where people can use their knowledge or sensory experiences of phenomena to valuate necessary truths or negate the possibility or necessity of its truthfulness. The theorist also uses this perspective to express the existing link between modal concepts and the standard classical predicate (Lean 104). For instance, the example of women who give birth being female can be explained by Quine as showing that the modal concepts can be combined with the standard predictate logic (Lean 104). For example, all women are female; hence 5 women who give birth to children are five female human beings. From the statement it can be said that 5 is more than 3, but the sentence more than 3 women who have given birth to children are female is logically possible but not necessary truth. The explanation being that more than 5 women or less than 3 women can give birth, and they will all be women.

On the other hand, Kripke significantly based his definition of necessary truth on the concept of rigid designators (Lean 104). The theorists focused on expressing existing distinctions which many other philosophers including Quine had failed to express. For instance, Kripke’s argument based on the example of the colors in the rainbow can be seen as questioning, why 7 is considered as being necessarily true, yet the statement that the number of colors in the rainbow is more than 5 is not considered as a necessary truth. Kripke expresses that necessary truth should not have to be rigid, and that flexibility of statement of identity allows for more objective necessary truths (Lean 104). For example it can be considered that there is a possibility that the numbers of colors in the rainbow are more than 7 and when this is so, then the statement that the rainbow has 7 colors will be rendered as not having rigid designators.

According to Kripke, other ways of describing statements of identity are not as rigid as the proper names. He expressed rigid designators as expressions that can be considered as universal everywhere (Lean 104). Hence aspects such as the number of letters in the alphabet is not a rigid designators because different languages across the globe have different alphabets and they are different in number, for example the number of alphabets in the Chinese language are different from the number of alphabets in the English language. Kripke’s theory consideration of metaphysical and the epistemological notion of necessary truths heightens skepticism (Lean 105). This is because when compared to Quine’s perspectives, Kripke’s approach is seen as raising doubts by emphasizing on the possibility of the existence of parallel truths which are of slight difference with the present truths. For example his theory focuses on the possibility that there is a possibility that the number of colors of the rainbow are more or less than 7.

Another significant example that can be used to effectively show how Quine’s consideration of metaphysical and the epistemological notion of necessary truths mitigates skepticism and expresses the combination of the modal concepts and the standard predictate logic as postulated by Quine is:

  • The rainbow is made up of 7 colors
  • 7 >5
  • The number of colors in the rainbow is more than 5

The above statements in accordance with Quine’s postulation of necessary truth can be taken to mean that it is true that the rainbow is made up of 7 colors. It is necessarily true that 7 is greater than 5. However, the statement that the number of colors in the rainbow is greater than 7 is not accurate or possible because it is non-necessary. The statement is dependent on the accuracy of the first two statements for its accuracy (Lean 103). Hence on its own, it can be deemed false because there is a possibility that the number of colors in the rainbow is less than 5, however, the use of the first two necessary truths makes the third statement true. The main explanation that was offered by Quine in relation to this factor is that when a statement of identity is existent with an identity sign flanked on either of its sides by a singular term, the principle of substitutivity confers that the statement is true and accurate if one of its two terms can be substituted for the other (Lean 105). His proposal also states that a statement can be considered as a necessary truth if its objects can be expressed in a purely referential way. Quine further stated that if the terms or objects are not expressed in a direct or purely referential way, then they are referential opacity, hence not necessary truths (Lean 107).

According to Martin Lean, necessary truth can be considered as a postulation that cannot be based on deceit (Lean 102). This means that necessary truth is truth that will constantly remain as the truth no matter the circumstances that surrounds it. For example, the outcome of 2 + 2 = 4 is expected to be the same even in a possible parallel realm. The metaphysical notion of necessary truth provides that truth can be based on the aspect that it is neither necessarily true nor false; hence it is based on the prevailing perceptions, scientific methods and approaches to logic (Lean 102). These approaches are likely to change with the passage of time. Hence what is truth today can become false tomorrow and what is false today can become true tomorrow. On the other hand, epistemological notion of necessary truth is based on the concept of analyticity. Analytic truths are based on the concept of the subjects under consideration being static (Lean 102). For instance, a mother who gives birth being a female is certain. This is because females are the only human beings that are capable of giving birth.

From the above perspective it can be seen that Martin’s consideration of metaphysical and the epistemological notion of necessary truths can be effectively explained through the understanding of the empiricism theory of truth (Lean 106). Martin expresses that truth is derived from sensory experiences, but it can also be arrived at through appropriate use of scientific approaches (Lean 107). The approaches gradually evolve and as a result truth becomes dependent on the changes to its representational properties as expressed by their analytical or scientific method determinants.



The source of knowledge and experience is a significant subject of discussion in philosophy. Different researchers and theorists have different definitions of what knowledge is and how it can be acquired. There also exists different hypothesis of the actual sources of knowledge (Lockard 20). One considerable source of knowledge according to many theorists is empiricism. Empiricism has been defined as a theory that stipulates that the sole source of knowledge is sensory experience. This definition has been simplified to mean that knowledge results from experience. What this means is that sense perception is the main source of knowledge. A considerable subject for debate by many theorists has always been that the study of human knowledge cannot be achieved in the absence of experience (Lockard 90). This theory has been used to explain that the older the world gets, the more knowledge its human population are able to accrue due to increased experiences (Lockard 96). The empirical approach to knowledge places considerable emphasis on the role that evidence plays in the development of knowledge. With regards to perceptions as presented by Martin, the experiences that people have are what results in the creation of awareness of mind-dependent objects that have properties which have representational properties (Lean 14). From this perspective, knowledge can be regarded as truth. The theorist also uses this perception to present that hallucination can to a great extent be linked to formation of ideas (Lean 14). The explanation offered is that ideas are at times based on the veridical hallucination of ordinary objects which may necessarily be present at the time when they are being perceived (Lean 15).

Martin’s argument points out that evidence can be obtained through experiments. This is because scientific methods, theories and hypothesis can all be tested using various approaches including observation (Lockard 96). This perspective can also be taken to mean that knowledge can only be arrived at through testing, hence what has not been tested cannot constitute as knowledge. This is one of the biggest weaknesses of the empiricism theory. The theory also contradicts Martin’s debate about hallucination because hallucinations are based on veridical perceptions, and not perceptions that are based on visually evident objects (Lockard 98). Empiricists usually consider that innate knowledge does not exist. According to the theorists, including Locke, Berkeley, and Hume, rationalism is not effective. A good example of how information cannot be rational is that illusions that people have cannot necessarily be representative of reality. For instance, the rational thinking that people can have that a ninth planet exists in Earth’s solar system cannot be taken to mean that the solar system has 9 planets. This was recently made evident when after considerable examination it was determined that Pluto which was once considered as the planet furthest from the sun was determined as not being a planet. The other significant perspective that arises from this argument is that knowledge keeps on evolving with the constantly evolution of scientific methods, theories, hypothesis and falsification (Lean 5).

The main argument that empiricism is based on about knowledge constantly changing with the passage of time is again the very perspective that limits the accuracy of the theory (Lean 16). Empiricism is based on a rigid foundationalist approach which negates the fact that knowledge can have different sources such as intuition, reasoning and revelation (Lockard 98). The best example of how the theory of empiricism is limited is the technology industry. The industry constantly develops and introduces new products and services which cannot be arrived at through sensory experience. For instance, the continued development of the virtual world has been based on the intuition of innovative individuals who have chosen to reason beyond the confines of knowledge that have been stipulated by the empiricism theory (Lean 7).

A significant aspect of the empiricism theory that has considerable shortcomings is the empiricists’ view of arithmetical truths. Arithmetic truths are considered as being synthetic a priori by empiricists who consider that truth and knowledge is based on conceptual exclusion (Lean 17). This perspective is limited by the fact that it is based on particular conceptual exclusion techniques which are subjective. This can be explained to mean that the logical truths are not accurate because they are unable to objectively link ideas and perceptions of different individuals or groups (Lockard 16). For example, the arithmetic truth that the 25th day of the April is the 25th day of the 4th month is false. This is because different religions across the globe have different approaches when it comes to determining what day a particular day is in their calendar. A good example is that the New Year in China, among Muslims, and among Christians significantly differs. This perspective can be used to offer an argument of how Locke’s perspective that our experiences inform us about the nature of our reality is accurate, however it does not emphasize on the significant differences that exist when it comes to subjectivity of experience. This is because the arithmetical truth for someone or an individual may be different in another region or for other people.

From the above discussion it is evident that a significant argument that is against arithmetic truths is that it does not consider the aspect of subjective. Empiricists consider that the theory is objective, they however make considerations of the fact that it is rigid and the possibility of truth/knowledge of a particular phenomena existing with different representational features (Lean 7). Another significant argument that is linked to this argument is that the theory limits the existence and spread of creativity. For instance, it is possible for similar logical truths to have different perspectives that offer explanations of its existence. A good explanation of this is that Plato once stated that with imagination and illusion, it is possible for man to construct their own reality (Lockard 56). In arithmetic truth this can be taken to mean that other than focusing on singular perspectives which includes the concepts of combining and separating things, it is possible to make new creations, for instance, developing new formulas that can be used to prove that 7 + 5 = 12.



(3.3) The sense data theory of perception introduced by Martin

Sense data has been a source of considerable interest in the sphere of philosophy for a long time now. Various different authors have presented different definitions of what sense data is. It is however notable that the different definitions include the term perception. This can be taken to mean that sense data cannot be explained without considering its link to perception. Martin introduced sense data as mind-dependent objects that have properties that they appear to have, and people are directly aware of in perception (Lean 3). This explanation is best used for physically observable objects which have traits and conditions which are formed in one’s mind. The image about objects that people form in their mind is usually based on the features of the object (Lean 3). For example many theorists have postulated that when individuals view a green apple, they usually base their perception of the object (apple) on its features such as color, shape and size. This mental image that people get to develop in their mind is what Martin considers as being ‘sense datum (Lean 3). Some of the most common criticism of sense data include that it is based on direct awareness of physical phenomena, yet offers limited explanations of phenomena that are not physical in nature. What is more is that the notion of sense data does not offer precise properties of the mental phenomena involved may not be constant (Lockard 105). For instance, apples may vary in sizes and colors. Another common conception that critics use is that the sense data may result in individuals having particular visual experience for instance, that of a green round apple, yet my experience is not itself green or round. Martin however presents that proponents of sense data have always argued that sense data is vital when it comes to offering explanations of phenomena as perspectival variation, illusion, and hallucination (Lockard 105). According to Martin, the sense data theory of perception usually offers succinct knowledge of the external world and its difficulty when it comes to locating sense data in physical space. It is a theory that is committed to the existence of objects with definite properties.

According to Martin the ‘problem of perception’ with regards to the sense data theory of perception is that the sense data is not necessarily a sensation (Lean 3). Martin believes that the problem of perception usually results from the phenomena of illusion and hallucination. According to the theorist, these errors in perception usually make it difficult to understand how perception can be related to openness and awareness of the world (Lean 6). Martin strongly believes that sense data is dependent of the mind and that the representational properties of objects are what evoke perceptions of direct awareness (Lean 8).

Hallucination is considered as a veridical perception of an ordinary object which is not present at the time it is being perceived. Based on the fact that it involves the veridical perception of ordinary object, many authors including Martin considers that hallucination does not involve deception (Lean 4). Martin also believes that hallucinations do not have to be similar to the ones that are being experienced by individuals who are mentally ill or use drugs and alcohol. They are however expected to be representations of possibilities. It is this view point that Martin uses to debate that individuals may at a point in time have an experience which is subjectively indistinguishable from the hallucinations that they have once had (Lockard 96).

Awareness is one of the core arguments that Martin presented in his argument of the sense data theory of perception. With regards to Martin’s presentation of awareness, hallucination cannot be considered as creating awareness of ordinary objects (Lockard 96). This is because people are not usually perceptually aware of ordinary objects whenever they are having veridical experiences; however, there veridical experiences are inclined towards objects that are ordinary in nature. Awareness according to Martin is perceptual experience that centers on the genuine perceptual contact of individuals, in relation to their contact with the world. It can be considered as the ordinary way of thinking about perceptual experience (Lean 5). Martin links awareness to hallucination by stating that hallucinations are developed from the perceptual awareness of ordinary mind-independent objects (Lean 5). The notion of awareness in the same breadth contradicts hallucination because hallucination is veridical perception of representational properties which are not available at the time of the perception, or exist in different forms from the existing representational properties in the veridical perception. This is while awareness is perception that is dependent on visually evident representational properties. The distinction between the two can be based on the awareness of a car burning being different from how the same car burns in a hallucination (Lean 8). This means that Martins consideration of hallucination being a veridical perception of an ordinary object is skewed (Lean 8). Because the hallucination that a person has of a car burning up after being lit, may quite different from how the car will actually burn, even though both instances contain the same representational properties, the nature of the properties is not similar for both examples.

In his theory, Martin focuses on the concept of awareness in relation to perception being rational. He as a result focused his theory of the relationship between perception and visual awareness (Lean 9). Though this perspective can be considered as being effective and relevant in that it can be used to argue that perceptual experience is relational, it fails to encompass the consideration of perceptions that are based on objects that do not have representational properties (Lean 7). A good example of this is the representation of Utopia. The explanation of this is that a utopian society is considered as being a community or society that is theoretical in nature. The society possesses highly desirable qualities and principles. However it lacks method and structure of how it can be implemented. This means that the awareness of utopia can be theoretical but not abstract. It also means that Martin’ sense data theory of perception is not effective when it comes to offering explanations of the explanations and the link between hallucination and awareness (Lean 6). For example, the explanation of the characteristics and qualities of utopia will generate different perceptions from different individuals because utopia lacks representational properties which Martin proposes are necessary, in his sense data theory of perception.


Works Cited

Lean, Martin. Sense-Perception And Matter: A Critical Analysis Of C D Broad’s Theory of Perception. Westport, Conneccticut: Greenwood Press, 1973.

Lockard, Matthew Korthase. Foundations of Epistemic Normativity. Los Angeles: University of Carlifornia, 2011.


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