A Legisign is a law that is a Sign. This law is usually [sic] established by men. Every conventional sign is a legisign. It is not a single object, but a general type which, it has been agreed, shall be significant. Every legisign signifies through an instance of its application, which may be termed a Replica of it. Thus, the word ‘the’ will usually occur from fifteen to twenty-five times on a page. It is in all these occurrences one and the same word, the same legisign. Each single instance of it is a Replica. The Replica is a Sinsign. Thus, every Legisign requires Sinsigns. But these are not ordinary Sinsigns, such as are peculiar occurrences that are regarded as significant. Nor would the Replica be significant if it were not for the law which renders it so.
In some sense, it is a strange fact that this first and basic trichotomy has not been widely discussed in relation to the continuity concept in Peirce, because it is crucial. It is evident from the second noticeable locus where this trichotomy is discussed, the letters to Lady Welby – here Peirce continues (after an introduction which brings less news):
The difference between a legisign and a qualisign, neither of which is an individual thing, is that a legisign has a definite identity, though usually admitting a great variety of appearances. Thus, &, and, and the sound are all one word. The qualisign, on the other hand, has no identity. It is the mere quality of an appearance and is not exactly the same throughout a second. Instead of identity, it has great similarity, and cannot differ much without being called quite another qualisign.
The legisign or type is distinguished as being general which is, in turn, defined by continuity: the type has a ‘great variety of appearances’; as a matter of fact, a continuous variation of appearances. In many cases even several continua of appearances (as &, and, and the spoken sound of ‘and’). Each continuity of appearances is gathered into one identity thanks to the type, making possible the repetition of identical signs. Reference is not yet discussed (it concerns the sign’s relation to its object), nor is meaning (referring to its relation to its interpretant) – what is at stake is merely the possibility for a type to incarnate a continuum of possible actualizations, however this be possible, and so repeatedly appear as one and the same sign despite other differences. Thus the reality of the type is the very foundation for Peirce’s ‘extreme realism’, and this for two reasons. First, seen from the side of the sign, the type provides the possibility of stable, repeatable signs: the type may – opposed to qualisigns and those sinsigns not being replicas of a type – be repeated as a self-identical occurrence, and this is what in the first place provides the stability which renders repeated sign use possible. Second, seen from the side of reality: because types, legisigns, are realized without reference to human subjectivity, the existence of types is the condition of possibility for a sign, in turn, to stably refer to stably occurring entities and objects. Here, the importance of the irreducible continuity in philosophy of mathematics appears for semiotics: it is that which grants the possibility of collecting a continuum in one identity, the special characteristic of the type concept. The opposition to the type is the qualisign or tone lacking the stability of the type – they are not self-identical even through a second, as Peirce says – they have, of course, the character of being infinitesimal entities, about which the principle of contradiction does not hold. The transformation from tone to type is thus the transformation from unstable pre-logic to stable logic – it covers, to phrase it in a Husserlian way, the phenomenology of logic. The legisign thus exerts its law over specific qualisigns and sinsigns – like in all Peirce’s trichotomies the higher sign types contain and govern specific instances of the lower types. The legisign is incarnated in singular, actual sinsigns representing the type – they are tokens of the type – and what they have in common are certain sets of qualities or qualisigns – tones – selected from continua delimited by the legisign. The amount of possible sinsigns, tokens, are summed up by a type, a stable and self-identical sign. Peirce’s despised nominalists would to some degree agree here: the universal as a type is indeed a ‘mere word’ – but the strong counterargument which Peirce’s position makes possible says that if ‘mere words’ may possess universality, then the world must contain it as well, because words are worldly phenomena like everything else. Here, nominalists will typically exclude words from the world and make them privileges of the subject, but for Peirce’s welding of idealism and naturalism nothing can be truly separated from the world – all what basically is in the mind must also exist in the world. Thus the synthetical continuum, which may, in some respects, be treated as one entity, becomes the very condition of possibility for the existence of types.
Whether some types or legisigns now refer to existing general objects or not is not a matter for the first trichotomy to decide; legisigns may be part of any number of false or nonsensical propositions, and not all legisigns are symbols, just like arguments, in turn, are only a subset of symbols – but all of them are legisigns because they must in themselves be general in order to provide the condition of possibility of identical repetition, of reference to general objects and of signifying general interpretants.