semiosis (from Greek semeiosis, ‘observation of signs’), the relation of signification involving the three relata of sign, object, and mind. Semiotic is the science or study of semiosis. The semiotic of John of Saint Thomas and of Peirce includes two distinct components: the relation of signification and the classification of signs. The relation of signification is genuinely triadic and cannot be reduced to the sum of its three subordinate dyads: sign-object, sign-mind, object-mind. A sign represents an object to a mind just as A gives a gift to B. Semiosis is not, as it is often taken to be, a mere compound of a sign-object dyad and a sign-mind dyad because these dyads lack the essential intentionality that unites mind with object; similarly, the gift relation involves not just A giving and B receiving but, crucially, the intention uniting A and B.
In the Scholastic logic of John of Saint Thomas, the sign-object dyad is a categorial relation (secundum esse), that is, an essential relation, falling in Aristotle’s category of relation, while the sign-mind dyad is a transcendental relation (secundum dici), that is, a relation only in an analogical sense, in a manner of speaking; thus the formal rationale of semiosis is constituted by the sign-object dyad. By contrast, in Peirce’s logic, the sign-object dyad and the sign-mind dyad are each only potential semiosis: thus, the hieroglyphs of ancient Egypt were merely potential signs until the discovery of the Rosetta Stone, just as a road-marking was a merely potential sign to the driver who overlooked it.
Classifications of signs typically follow from the logic of semiosis. Thus John of Saint Thomas divides signs according to their relations to their objects into natural signs (smoke as a sign of fire), customary signs (napkins on the table as a sign that dinner is imminent), and stipulated signs (as when a neologism is coined); he also divides signs according to their relations to a mind. An instrumental sign must first be cognized as an object before it can signify (e.g., a written word or a symptom); a formal sign, by contrast, directs the mind to its object without having first been cognized (e.g., percepts and concepts). Formal signs are not that which we cognize but that by which we cognize. All instrumental signs presuppose the action of formal signs in the semiosis of cognition. Peirce similarly classified signs into three trichotomies according to their relations with (1) themselves, (2) their objects, and (3) their interpretants (usually minds); and Charles Morris, who followed Peirce closely, called the relationship of signs to one another the syntactical dimension of semiosis, the relationship of signs to their objects the semantical dimension of semiosis, and the relationship of signs to their interpreters the pragmatic dimension of semiosis.
See also JOHN OF SAINT THOMAS, PEIRCE, THEORY OF SIGN. J.B.M.