Triadic relation

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In logic, mathematics, and semiotics, a triadic relation is an important special case of a polyadic or finitary relation, one in which the number of places in the relation is three. In other language that is often used, a triadic relation is called a ternary relation. One may also see the adjectives 3-adic, 3-ary, 3-dimensional, or 3-place being used to describe these relations.

Mathematics is positively rife with examples of 3-adic relations, and a sign relation, the arch-idea of the whole field of semiotics, is a special case of a 3-adic relation. Therefore it will be useful to consider a few concrete examples from each of these two realms.

Examples from mathematics
For the sake of topics to be taken up later, it is useful to examine a pair of 3-adic relations in tandem, $$L_0\!$$ and $$L_1,\!$$ that can be described in the following manner.

The first order of business is to define the space in which the relations $$L_0\!$$ and $$L_1\!$$ take up residence. This space is constructed as a 3-fold cartesian power in the following way.

The boolean domain is the set $$\mathbb{B} = \{ 0, 1 \}.\!$$

The plus sign $${}^{\backprime\backprime} + {}^{\prime\prime},\!$$ used in the context of the boolean domain $$\mathbb{B},\!$$ denotes addition modulo 2. Interpreted for logic, the plus sign can be used to indicate either the boolean operation of exclusive disjunction, $$\mathrm{XOR} : \mathbb{B} \times \mathbb{B} \to \mathbb{B},\!$$ or the boolean relation of logical inequality, $$\mathrm{NEQ} \subseteq \mathbb{B} \times \mathbb{B}.\!$$

The third cartesian power of $$\mathbb{B}\!$$ is the set $$\mathbb{B}^3 = \mathbb{B} \times \mathbb{B} \times \mathbb{B} = \{ (x_1, x_2, x_3) : x_j \in \mathbb{B} ~\text{for}~ j = 1, 2, 3 \}.\!$$

In what follows, the space $$X \times Y \times Z\!$$ is isomorphic to $$\mathbb{B} \times \mathbb{B} \times \mathbb{B} ~=~ \mathbb{B}^3.\!$$

The relation $$L_0\!$$ is defined as follows:

The relation $$L_0\!$$ is the set of four triples enumerated here:

The relation $$L_1\!$$ is defined as follows:

The relation $$L_1\!$$ is the set of four triples enumerated here:

The triples that make up the relations $$L_0\!$$ and $$L_1\!$$ are conveniently arranged in the form of relational data tables, as follows:

Examples from semiotics
The study of signs &mdash; the full variety of significant forms of expression &mdash; in relation to the things that signs are significant of, and in relation to the beings that signs are significant to, is known as semiotics or the theory of signs. As just described, semiotics treats of a 3-place relation among signs, their objects, and their interpreters.

The term semiosis refers to any activity or process that involves signs. Studies of semiosis that deal with its more abstract form are not concerned with every concrete detail of the entities that act as signs, as objects, or as agents of semiosis, but only with the most salient patterns of relationship among these three roles. In particular, the formal theory of signs does not consider all of the properties of the interpretive agent but only the more striking features of the impressions that signs make on a representative interpreter. In its formal aspects, that impact or influence may be treated as just another sign, called the interpretant sign, or the interpretant for short. Such a 3-adic relation, among objects, signs, and interpretants, is called a sign relation.

For example, consider the aspects of sign use that concern two people &mdash; let us say $$\mathrm{Ann}\!$$ and $$\mathrm{Bob}\!$$ &mdash; in using their own proper names, $${}^{\backprime\backprime} \mathrm{Ann} {}^{\prime\prime}\!$$ and $${}^{\backprime\backprime} \mathrm{Bob} {}^{\prime\prime},\!$$ together with the pronouns, $${}^{\backprime\backprime} \mathrm{I} {}^{\prime\prime}\!$$ and $${}^{\backprime\backprime} \mathrm{you} {}^{\prime\prime}.\!$$ For brevity, these four signs may be abbreviated to the set $$\{ \, {}^{\backprime\backprime} \mathrm{A} {}^{\prime\prime}, \, {}^{\backprime\backprime} \mathrm{B} {}^{\prime\prime}, \, {}^{\backprime\backprime} \mathrm{i} {}^{\prime\prime}, \, {}^{\backprime\backprime} \mathrm{u} {}^{\prime\prime} \, \}.\!$$  The abstract consideration of how $$\mathrm{A}\!$$ and $$\mathrm{B}\!$$ use this set of signs to refer to themselves and each other leads to the contemplation of a pair of 3-adic relations, the sign relations $$L_\mathrm{A}\!$$ and $$L_\mathrm{B},\!$$ that reflect the differential use of these signs by $$\mathrm{A}\!$$ and $$\mathrm{B},\!$$ respectively.

Each of the sign relations, $$L_\mathrm{A}\!$$ and $$L_\mathrm{B},\!$$ consists of eight triples of the form $$(x, y, z),\!$$ where the object $$x\!$$ is an element of the object domain $$O = \{ \mathrm{A}, \mathrm{B} \},\!$$ where the sign $$y\!$$ is an element of the sign domain $$S\!,$$ where the interpretant sign $$z\!$$ is an element of the interpretant domain $$I,\!$$ and where it happens in this case that $$S = I = \{ \, {}^{\backprime\backprime} \mathrm{A} {}^{\prime\prime}, \, {}^{\backprime\backprime} \mathrm{B} {}^{\prime\prime}, \, {}^{\backprime\backprime} \mathrm{i} {}^{\prime\prime}, \, {}^{\backprime\backprime} \mathrm{u} {}^{\prime\prime} \, \}.\!$$ In general, it is convenient to refer to the union $$S \cup I\!$$ as the syntactic domain, but in this case $$S ~=~ I ~=~ S \cup I.\!$$

The set-up so far is summarized as follows:

The relation $$L_\mathrm{A}\!$$ is the set of eight triples enumerated here:

The triples in $$L_\mathrm{A}\!$$ represent the way that interpreter $$\mathrm{A}\!$$ uses signs. For example, the listing of the triple $$(\mathrm{B}, \, {}^{\backprime\backprime} \mathrm{u} {}^{\prime\prime}, \, {}^{\backprime\backprime} \mathrm{B} {}^{\prime\prime})\!$$ in $$L_\mathrm{A}\!$$ represents the fact that $$\mathrm{A}\!$$ uses $${}^{\backprime\backprime} \mathrm{B} {}^{\prime\prime}\!$$ to mean the same thing that $$\mathrm{A}\!$$ uses $${}^{\backprime\backprime} \mathrm{u} {}^{\prime\prime}\!$$ to mean, namely, $$\mathrm{B}.\!$$

The relation $$L_\mathrm{B}\!$$ is the set of eight triples enumerated here:

The triples in $$L_\mathrm{B}\!$$ represent the way that interpreter $$\mathrm{B}\!$$ uses signs. For example, the listing of the triple $$(\mathrm{B}, \, {}^{\backprime\backprime} \mathrm{i} {}^{\prime\prime}, \, {}^{\backprime\backprime} \mathrm{B} {}^{\prime\prime})\!$$ in $$L_\mathrm{B}\!$$ represents the fact that $$\mathrm{B}\!$$ uses $${}^{\backprime\backprime} \mathrm{B} {}^{\prime\prime}\!$$ to mean the same thing that $$\mathrm{B}\!$$ uses $${}^{\backprime\backprime} \mathrm{i} {}^{\prime\prime}\!$$ to mean, namely, $$\mathrm{B}.\!$$

The triples that make up the relations $$L_\mathrm{A}\!$$ and $$L_\mathrm{B}\!$$ are conveniently arranged in the form of relational data tables, as follows:

Focal nodes

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Peer nodes

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Logical operators

 * Exclusive disjunction
 * Logical conjunction
 * Logical disjunction
 * Logical equality


 * Logical implication
 * Logical NAND
 * Logical NNOR
 * Negation

Related topics

 * Ampheck
 * Boolean domain
 * Boolean function
 * Boolean-valued function
 * Differential logic


 * Logical graph
 * Minimal negation operator
 * Multigrade operator
 * Parametric operator
 * Peirce's law


 * Propositional calculus
 * Sole sufficient operator
 * Truth table
 * Universe of discourse
 * Zeroth order logic

Relational concepts

 * Continuous predicate
 * Hypostatic abstraction
 * Logic of relatives
 * Logical matrix


 * Relation
 * Relation composition
 * Relation construction
 * Relation reduction


 * Relation theory
 * Relative term
 * Sign relation
 * Triadic relation

Information, Inquiry

 * Inquiry
 * Dynamics of inquiry


 * Semeiotic
 * Logic of information


 * Descriptive science
 * Normative science


 * Pragmatic maxim
 * Truth theory

Related articles

 * Cactus Language
 * Futures Of Logical Graphs
 * Propositional Equation Reasoning Systems


 * Differential Logic : Introduction
 * Differential Propositional Calculus
 * Differential Logic and Dynamic Systems


 * Introduction to Inquiry Driven Systems
 * Prospects for Inquiry Driven Systems
 * Inquiry Driven Systems : Inquiry Into Inquiry

Document history
Portions of the above article were adapted from the following sources under the GNU Free Documentation License, under other applicable licenses, or by permission of the copyright holders.


 * Triadic Relation, InterSciWiki
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 * Triadic Relation, PlanetMath
 * Triadic Relation, Wikinfo
 * Triadic Relation, Wikiversity
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 * Triadic Relation, Wikipedia