Charles S. Peirce’s theory of signs is a theory of reasoning and of cognition which asserts that all modes of thinking depend on the use of signs. Peirce argues that every thought is a sign, and that every act of reasoning consists of the interpretation of signs. Signs function as mediators between the external world of objects and the internal world of ideas. Signs may be mental representations of objects, and objects may be known by means of perception of their signs. Peirce thus defines ‘semiosis’ as the process by which representations of objects function as signs. Semiosis is a process of cooperation between signs, their objects, and their ‘interpretants’ (i.e. their mental representations). ‘Semiotic’ (i.e. the science of signs) is the study of semiosis and is an inquiry into the conditions which are necessary in order for representations of objects to function as signs.
Peirce describes logic as the science of the laws of signs, and divides logic into three areas of study: 1) ‘critical logic’ (i.e. the study of the relations of signs to their objects), 2) ‘speculative grammar’ (i.e. the study of the 'meaning' of signs), and 3) ‘speculative rhetoric’ or ‘methodeutic’ (i.e. the study of the relation of signs to their interpretants). Logic as semiotic is the theory of the conditions which determine the truth of signs, and is a normative science, in that it is a theory of the kind of reasoning which should be employed in order to discover truth.
Peirce argues that every science may be defined by the range of problems with which it is concerned, and that every science may be described as either: 1) a science of discovery, 2) a theoretical science, or 3) a practical science. The sciences of discovery may include: mathematics, philosophy, physical sciences, psychological sciences, and social sciences. The theoretical sciences may include: 1) the sciences of discovery, and 2) the sciences which arrange the results of discovery or which produce the philosophy of science. The practical sciences may include all of the other sciences which are devoted to practical purposes (such as the vocational, industrial, and technological sciences).
Peirce explains that philosophy may be divided into three areas of study: 1) phenomenology (i.e. the study of phenomena as objects of perception), 2) normative science (i.e. the study of the proper relations of phenomena), and 3) metaphysics (i.e. the study of the nature of ultimate reality). Normative science may be divided into: 1) aesthetics (i.e. the science of ideals), 2) ethics (i.e. the science of right and wrong conduct), and 3) logic (i.e. the science of the laws of thought).1
Peirce also explains that while phenomenology is the study of phenomena in their ‘Firstness,’ normative science is the study of phenomena in their ‘Secondness,’ and metaphysics is the study of phenomena in their ‘Thirdness’ (CP 5.122-124).2 Firstness, Secondness, and Thirdness are the three ‘categories’ or ‘modes of being’ which give meaning to all phenomena and to all objects of thought. All phenomena may be regarded as manifestations of either Firstness, Secondness, or Thirdness.
According to Peirce, ‘meaning’ is a triadic relation between a sign, an object, and an interpretant. This triadic relation is not reducible to a set of dyadic relations between a sign and an object or between an object and an interpretant (CP 1.345). Meaning is never reducible to Firstness or Secondness, but can only be a ‘genuine’ Thirdness. A general meaning can always be found in ‘genuine’ triadic relations, but can never be found in ‘degenerate’ triadic relations which have lost their Thirdness.
Peirce describes Firstness as the mode of being of that which is without reference to any subject or object. Secondness is the mode of being of that which is itself in referring to a second subject, regardless of any third subject. Thirdness is the mode of being of that which is itself in bringing a second and a third subject into relation with each other (CP 8.328).3 Thirdness brings Firstness and Secondness into relation with each other, and mediates between them. Thirdness is the mode of being of signs, in that signs mediate relations between their objects and their interpretants.
Peirce explains that Firstness may be manifested by quality, feeling, freedom, or multiplicity. Secondness may be manifested by action, reaction, causality, reality, actuality, or factuality. Thirdness may be manifested by representation, thought, continuity, order, unity, or generality.
Peirce argues that Firstness does not have any Secondness or Thirdness, but that Secondness and Thirdness each have their own Firstness (CP 1.530). Firstness is the mode of being a quality but not a relation. Secondness may define dyadic relations, but Thirdness may define triadic, tetradic, pentadic, and other plural relations. Firstness is the mode of being a possibility, but Secondness is the mode of being a fact, and Thirdness is the mode of being a sign or representation.
Peirce also argues that while Secondness and Thirdness may be either ‘genuine’ or ‘degenerate,’ Firstness is not susceptible to ‘degeneracy.'4 ‘Genuine’ Secondness is a Firstness to be Second, but ‘degenerate’ Secondness is a Secondness to Firstness (CP 1. 528). ‘Genuine’ Thirdness is a Thirdness which bring Firstness and Secondness into relation with each other as modes of thought. ‘Genuine’ Thirdness determines the nature of both Firstness and Secondness, so that Firstness is a mode of thought as possibility, Secondness is a mode of thought as actuality, and Thirdness is s mode of thought as law or representation. ‘Degenerate’ Thirdness, on the other hand, may be a Thirdness which regards Secondness as a fact rather than as a mode of thought or of representation. This is called by Peirce the first ‘degree’ or ‘grade’ of ‘degenerate’ Thirdness. ‘Degenerate’ Thirdness may also be a Thirdness which does not include a true Secondness but which regards Firstness as representing itself to itself. This is called by Peirce the second ‘degree’ or ‘grade’ of ‘degenerate’ Thirdness (CP 5.70-71).
Peirce describes ‘genuine’ Thirdness as a triadic relation in which an object is referred to by a sign and by an interpretant. He describes a sign (or ‘representamen’) as anything which denotes an object, and he defines an object as anything which can be thought. He defines an interpretant as the mental effect of a sign and as the ‘signification’ or ‘interpretation’ of the sign (CP 8.184).5 The interpretant is itself a sign which may have a triadic relation with the sign which it signifies and with its own interpretant. Thus, the triadic relation between a sign, an object, and an interpretant may be repeated infinitely (CP 2.303).6
Peirce explains that the object of a sign may be either an 'immediate object' (i.e. an object as represented by a sign) or a 'dynamical object' (i.e. an object as the actual cause of a sign). Similarly, the interpretant of a sign may be either an ‘immediate interpretant’ (i.e. an interpretant as represented by a sign), a ‘dynamical interpretant’ (i.e. the interpretant which is actually produced by a sign), or a ‘final interpretant’ (i.e. the interpretant which would be produced if the sign were properly understood).7
Peirce defines the ‘ground’ of a sign as the idea or principle which determines how the sign represents its object (CP 2.228). The triadic relation between the ground, object, and interpretant of a sign may have its own signification, which may produce another triadic relation between the relation itself, its signfication, and the interpretation of that signification.
Peirce also explains that a sign may be classified as either a ‘qualisign,’ a ‘sinsign,’ or a ‘legisign,’ according to its relation with its 'immediate object.' A ‘qualisign’ may be determined by its 'immediate object' because of internal properties of its own. A ‘sinsign’ may be determined by its 'immediate object' because of an actual relation with that object. A ‘legisign’ may be determined by its 'immediate object' because it is interpreted to be a sign of that object.
According to Peirce, a ‘qualisign’ is a quality which acts as a sign, a ‘sinsign’ (or ‘token’) is an actually existing thing or event which acts as a sign, and a ‘legisign’ is a law which acts as a sign.8 This is the First Trichotomy of Signs. A ‘qualisign’ corresponds to the category of Firstness, a ‘sinsign’ corresponds to the category of Secondness, and a ‘legisign’ corresponds to the category of Thirdness.
Peirce explains that a sign may be classified as either an ‘icon,’ an ‘index,’ or a ‘symbol,’ according to its relation with its 'dynamical object.' An ‘icon’ (such as a picture, image, model, or diagram) is a sign which itself demonstrates the qualities of its 'dynamical object.' An ‘index’ or ‘seme’ (such as a clock, thermometer, fuel gauge, or medical symptom) is a sign which demonstrates the influence of its 'dynamical object.' A ‘symbol’ (such as a trophy, medal, receipt, diploma, monument, word, phrase, or sentence) is a sign which is interpreted to be a reference to its 'dynamical object.' This is the Second Trichotomy of Signs. An ‘icon’ corresponnds to the category of Firstness, an ‘index’ corresponds to the category of Secondness, and a ‘symbol’ corresponds to the category of Thirdness.
Peirce also explains that a sign may be classified as either a ‘rheme,’ a ‘dicisign,’ or an ‘argument,’ according to its relation with its interpretant. A ‘rheme’ is interpreted as a sign of qualitative possibility, a ‘dicisign’ (or ‘dicent sign’) is interpreted as a sign of actual existence, and an ‘argument’ is interpreted as a sign of a law (or of a necessary truth).9 This is the Third Trichotomy of Signs. A ‘rheme’ corresponds to the category of Firstness, a ‘dicisign’ corresponds to the category of Secondness, and an ‘argument’ correponds to the category of Thirdness.
Peirce notes that a sign may refer to more than one object or group of objects (CP 2.230).10 A sign may be an element of another sign, or may itself be composed of other signs. A sign may refer to a simple object, or may refer to a complex object. A sign may have a simple meaning, or may have a complex meaning. The meaning of a sign may be determined by its relations with other signs.
Peirce argues that some signs may act through other signs. For example, ‘symbols’ and ‘legisigns’ may act through ‘sinsigns.’ ‘Sinsigns’ may be ‘Replicas’ (i.e. individual examples) of ‘symbols’ and ‘legisigns.’
Peirce describes ten classes of signs which may be produced by triads of simple signs. Each of the ten classes of signs may correspond to a distinct triadic relation between the categories of Firstness, Secondness, and Thirdness. Thus, the classification table shows that: 1) ‘qualisigns’ correspond to the relation of Firstness-Firstness-Firstness, 2) ‘iconic sinsigns’ correpond to the relation of Firstness-Firstness-Secondness, 3) ‘rhematic indexical sinsigns’ correspond to the relation of Firstness-Secondness-Secondness, 4) ‘dicent sinsigns’ correspond to the relation of Secondness-Secondness-Secondness, 5) ‘iconic legisigns’ correspond to the relation of Firstness-Firstness-Thirdness, 6) ‘rhematic indexical legisigns’ correspond to the relation of Firstness-Secondness-Thirdness, 7) ‘dicent indexical legisigns’ correspond to the relation of Secondness-Secondness-Thirdness, 8) ‘rhematic symbols’ correspond to the relation of Firstness-Thirdness-Thirdness, 9) ‘dicent symbols’ correspond to the relation of Secondness-Thirdness-Thirdness, and 10) ‘arguments’ correspond to the relation of Thirdness-Thirdness-Thirdness.
Peirce explains that to designate a ‘qualisign’ as a ‘rhematic iconic qualisign’ is redundant, because a ‘qualisign’ can only be ‘rhematic’ and ‘iconic.’ Similarly, to designate an ‘iconic sinsign’ as a ‘rhematic iconic sinsign’ is redundant, because an ‘iconic sinsign’ can only be ‘rhematic.’ To designate a ‘dicent symbol’ as a ‘dicent symbol legisign’ is redundant, because every symbol is a legisign.
Peirce defines a ‘qualisign’ (such as hardness, softness, warmth, coldness) as any quality which acts as a sign. An ‘iconic sinsign’ (such as a photograph or a diagram) is a representation or likeness of an actually existing thing or event. A ‘rhematic indexical sinsign’ (such as a cry in the street) is a sign which directs attention to the object by which it is caused. A ‘dicent sinsign’ (such as a bullet hole in a wall, or the motion of a weathervane) is a sign which demonstrates the influence of its object. An ‘iconic legisign’ (such as a map or a diagram) is any general law or set of principles which itself demonstrates the qualities of the object to which it refers. A ‘rhematic indexical legisign’ (such as a knock on the door or the ringing of a telephone) is any general law which requires each manifestation of it to demonstrate the influence of the object to which it refers, thus attracting attention to that object. A ‘dicent indexical legisign’ (such as the manner in which a person behaves, or the manner in which a person communicates with others) is any general law which requires each manifestion of it to demonstrate the influence of the object to which it refers, thus providing specific information about that object. A ‘rhematic symbol’ (such as a badge, an emblem, a uniform, or a flag) is a sign which may be interpreted to refer to a general concept. A ‘dicent symbol’ (such as a proposition or a description) is a sign which may be interpreted to refer to an actually existing object. An ‘argument’ (such as a syllogism) is a sign of a general law or of a conclusion which leads to the truth.11
Peirce also argues that if every thought is a sign, then every thought may be described as either an icon, an index, or a symbol. Icons and indices may be constituents of symbols. Symbols may be laws or general 'types' (i.e. 'legisigns'), and may be general terms which are used to produce concepts. Symbols may be conventional signs which are used as signs for other signs.
1Charles Sanders Peirce, Collected Papers of Charles Sanders Peirce, Volume I, paragraph 191, 1903 (Cambridge: Harvard University Press, 1960), p. 79.
2Ibid., Volume 5, paragraphs 122-124, 1903, p. 78.
3Ibid., Volume 8, paragraph 328, 1904, p. 220.
4Ibid., Volume 5, paragraph 68, 1903, p. 47.
5Ibid., Volume 8, paragraph 184, p. 139.
6Ibid., Volume 2, paragraph 303, 1903, p. 169.
7Ibid., Volume 8, paragraph 343, 1908, p. 232.
8Ibid., Volume 2, paragraphs 244-6, 1903, p. 142.
9Ibid., Volume 2, paragraphs 250-2, 1903, p. 144.
10Ibid., Volume 2, paragraph 230, 1910, p. 136.
11Ibid., Volume 2, paragraphs 254-263, 1903, pp.147-9.
Peirce, Charles Sanders. Collected Papers of Charles Sanders Peirce. Volumes I and II. Cambridge: Harvard University Press, 1960.
Peirce, Charles Sanders. Collected Papers of Charles Sanders Peirce. Volumes V and VI. Cambridge: Harvard University Press, 1960.
Peirce, Charles Sanders. Collected Papers of Charles Sanders Peirce. Volume VIII. Cambridge: Harvard University, Press, 1958.