Triadic relation

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, \(\operatorname{XOR} : \mathbb{B} \times \mathbb{B} \to \mathbb{B},\) or the boolean relation of logical inequality, \(\operatorname{NEQ} \subseteq \mathbb{B} \times \mathbb{B}.\)

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:

\[L_0 = \{ (x, y, z) \in \mathbb{B}^3 : x + y + z = 0 \}.\]

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

\[L_0 = \{ (0, 0, 0), (0, 1, 1), (1, 0, 1), (1, 1, 0) \}.\!\]

The relation \(L_1\!\) is defined as follows:

\[L_1 = \{ (x, y, z) \in \mathbb{B}^3 : x + y + z = 1 \}.\]

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

\[L_1 = \{ (0, 0, 1), (0, 1, 0), (1, 0, 0), (1, 1, 1) \}.\!\]

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

\(L_0 ~=~ \{ (x, y, z) \in \mathbb{B}^3 : x + y + z = 0 \}\)

\(X\!\)	\(Y\!\)	\(Z\!\)
\(0\!\)	\(0\!\)	\(0\!\)
\(0\!\)	\(1\!\)	\(1\!\)
\(1\!\)	\(0\!\)	\(1\!\)
\(1\!\)	\(1\!\)	\(0\!\)

\(L_1 ~=~ \{ (x, y, z) \in \mathbb{B}^3 : x + y + z = 1 \}\)

\(X\!\)	\(Y\!\)	\(Z\!\)
\(0\!\)	\(0\!\)	\(1\!\)
\(0\!\)	\(1\!\)	\(0\!\)
\(1\!\)	\(0\!\)	\(0\!\)
\(1\!\)	\(1\!\)	\(1\!\)

Examples from semiotics

The study of signs — the full variety of significant forms of expression — 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, say, Ann and Bob, in using their own proper names, "Ann" and "Bob", and in using the pronouns "I" and "you". For brevity, these four signs may be abbreviated to the set {"A", "B", "i", "u"}. The abstract consideration of how A and B use this set of signs to refer to themselves and to each other leads to the contemplation of a pair of 3-adic relations, the sign relations L_A and L_B, that reflect the differential use of these signs by A and by B, respectively.

Each of the sign relations, L_A and L_B, consists of eight triples of the form (x, y, z), where the object x belongs to the object domain O = {A, B}, where the sign y belongs to the sign domain S, where the interpretant sign z belongs to the interpretant domain I, and where it happens in this case that S = I = {"A", "B", "i", "u"}. In general, it is convenient to refer to the union S ∪ I as the "syntactic domain", but in this case S = I = S ∪ I.

The set-up to this point can be summarized as follows:

L_A, L_B ⊆ O × S × I

O = {A, B}

S = {"A", "B", "i", "u"}

I = {"A", "B", "i", "u"}

The relation L_A is the set of eight triples enumerated here:

{(A, "A", "A"), (A, "A", "i"), (A, "i", "A"), (A, "i", "i"),

 (B, "B", "B"), (B, "B", "u"), (B, "u", "B"), (B, "u", "u")}.

The triples in L_A represent the way that interpreter A uses signs. For example, the listing of the triple (B, "u", "B") in L_A represents the fact that A uses "B" to mean the same thing that A uses "u" to mean, namely, B.

The relation L_B is the set of eight triples enumerated here:

{(A, "A", "A"), (A, "A", "u"), (A, "u", "A"), (A, "u", "u"),

 (B, "B", "B"), (B, "B", "i"), (B, "i", "B"), (B, "i", "i")}.

The triples in L_B represent the way that interpreter B uses signs. For example, the listing of the triple (B, "i", "B") in L_B represents the fact that B uses "B" to mean the same thing that B uses "i" to mean, namely, B.

The triples that make up the relations L_A and L_B are conveniently arranged in the form of relational data tables, as follows:

L_A = Sign Relation of Interpreter A

Object	Sign	Interpretant
A	"A"	"A"
A	"A"	"i"
A	"i"	"A"
A	"i"	"i"
B	"B"	"B"
B	"B"	"u"
B	"u"	"B"
B	"u"	"u"

L_B = Sign Relation of Interpreter B

Object	Sign	Interpretant
A	"A"	"A"
A	"A"	"u"
A	"u"	"A"
A	"u"	"u"
B	"B"	"B"
B	"B"	"i"
B	"i"	"B"
B	"i"	"i"

See also

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• Relation
• Relation composition
• Relation construction
• Relation reduction
• Logic of relatives

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• Logical matrix
• Semeiotic
• Semiotic
• Semiotic information
• Sign relation

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Aficionados

• See Talk:Triadic relation for discussions/comments regarding this article.
• See Triadic relation/Aficionados for those who have listed Triadic relation as an interest.
• See Talk:Triadic relation/Aficionados for discussions regarding this interest.

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