Eco (in a 1981 article in The Bulletin of the Midwest MLA ) surveys the problems of sign theory. A fundamental objection to a general theory of signs is that the concept of “sign” is being used for things that are unlike: For linguistic signs that stand for the things they signify (in a p = q relation), as well as for symptoms from which a physician infers sickness (reasoning from effect to cause), for meteorological indications that enable us to predict the weather (reasoning from cause to effect), and other things. It’s illegitimate, so it is argued, to smush all of these different relations into a single relation of signifier-signified.
Eco finds an answer to this objection in Augustine’s de Magistro , and particularly in the discussion of the particle “ex.”
Augustine challenges Adeodatus to tell him what “ex” means, assuming what Eco identifies as a Stoic concept of the sign - that “every linguistic principle has a semantic correlate.” Adeodatus tries to say “ex” means “de,” but that only moves the question back a step. In Eco’s view, Augustine concludes that “ex” “represents a set of textual instructions,” and claims that the ingeniousness of this solution was lost to semiotic study until Saussure and the rise of structuralism.
If linguistic signs are textual instructions, then the relation of signifier to signified is not a p = q relation but implies an inferential relation between p and q. This helps to smooth out the different sorts of sign-relations that appear to be so different (but only because of the prejudice that linguistic signs are equivalences to the things they signify): “I should like to stress that such an instruction-like format is not limited to verbal texts but is rather typical of every sign system. A road signal meaning ‘stop,’ irrespective of the means of expression, whether alphabetical letters or some visual sign, should be interpreted as follows: if this expression is inserted into a road context x, then, if you are in a care, stop; if you have stopped, look carefully right and left, and then, if there is no danger, proceed. Or, if you do not stop and look, then face the possibilities of a fine.”
He has earlier claimed that linguistic signs have a pre-textual trajectory, but he also notes that when linguistic signs are seen as textual instructions the role of the interpreter comes to the fore, and the text is open to a proliferating variety of interpretations: “The reader plays an active role in interpretation because signs are structure according to an inferential model . . . . Textual interpretation is possible because even linguistic signs are not ruled by sheer equivalence (synonymy and definition); they are not based upon the idea of identify but are governed by an inferential schema; they are, therefore, infinitely interpretable. Texts can say more than on supposes, they can always say something new, precisely because signs are the starting point of a process of interpretation which leads to an infinite series of progressive consequences. Signs are open devices, not stiff armors prescribing a bi-conditional identity.”
When we read “John is a bachelor,” we are instructed to look around for contexts that will clarify what the word “bachelor” means (unmarried, without a graduate degree, a young man serving under a knight). We reason “abductively,” and Eco says that the “principle feature of a text is precisely its ability to elicit abductions.”