Digital Companion to C. S. Peirce
1868 | Some Consequences of Four Incapacities | W 2:223

…a sign has, as such, three references: 1st, it is a sign to some thought which interprets it; 2d, it is a sign for some object to which in that thought it is equivalent; 3d, it is a sign, in some respect or quality, which brings it into connection with its object.

1873 | On the nature of signs | W 3:66-8

A sign is an object which stands for another to some mind. I propose to describe the characters of a sign. In the first place like any other thing it must have qualities which belong to it whether it be regarded as a sign or not. Thus a printed word is black, has a certain number of letters and those letters have certain shapes. Such characters of a sign I call its material quality. In the next place a sign must have some real connection with the thing it signifies so that when the object is present or is so as the sign signifies it to be, the sign shall so signify it and otherwise not. [—] I shall term this character of signs their pure demonstrative application. In the 3rd place it is necessary for a sign to be a sign that it should be regarded as a sign for it is only a sign to that mind which so considers and if it is not a sign to any mind it is not a sign at all. It must be known to the mind first in its material qualities but also in its pure demonstrative application. That mind must conceive it to be connected with its object so that it is possible to reason from the sign to the thing. Let us now see what the appeal of a sign to the mind amounts to. It produces a certain idea in the mind which is the idea that it is a sign of the thing it signifies and an idea is itself a sign, for an idea is an object and it represents an object.

1873 | Logic. Chap. 5th | W 3:76; CP 7.355-6

a thing which stands for another thing is a representation or sign. So that it appears that every species of actual cognition is of the nature of a sign. [—]

Let us examine some of the characters of signs in general. A sign must in the first place have some qualities in itself which serve to distinguish it, a word must have a peculiar sound different from the sound of another word; but it makes no difference what the sound is, so long as it is something distinguishable. In the next place, a sign must have a real physical connection with the thing it signifies so as to be affected by that thing. A weather-cock, which is a sign of the direction of the wind, must really turn with the wind. This word in this connection is an indirect one; but unless there be some way or other which shall connect words with the things they signify, and shall ensure their correspondence with them, they have no value as signs of those things. Whatever has these two characters is fit to become a sign. It is at least a symptom, but it is not actually a sign unless it is used as such; that is unless it is interpreted to thought and addresses itself to some mind.

1885 | On the Algebra of Logic: A Contribution to the Philosophy of Notation | W 5:162

A sign is in a conjoint relation to the thing denoted and to the mind.

1893-5 [c.] | Chapter II: The Categories | NEM 4:309-10; CP 1.339

The easiest of those which are of philosophical interest is the idea of a sign, or representation. A sign stands for something to the idea which it produces, or modifies. Or, it is a vehicle conveying into the mind something from without. That for which it stands is called its Object; that which it conveys, its Meaning; and the idea to which it gives rise, its Interpretant. The object of representation can be nothing but a representation of which the first representation is the interpretant. But an endless series of representations, each representing the one behind it, may be conceived to have an absolute object at its limit. The meaning of a representation can be nothing but a representation. In fact, it is nothing but the representation itself conceived as stripped of irrelevant clothing. But this clothing never can be completely stripped off; it is only changed for something more diaphanous. So there is an infinite regression here. Finally, the interpretant is nothing but another representation to which the torch of truth is handed along; and as representation, it has its interpretant again. Lo, another infinite series.

1894 | The Art of Reasoning. Chapter II. What is a Sign? | EP 2:5; MS [R] 1009

There are three kinds of interest we may take in a thing. First, we may have a primary interest in it for itself. Second, we may have a secondary interest in it, on account of its reactions with other things. Third, we may have a mediatory interest in it, in so far as it conveys to a mind an idea about a thing. In so far as it does this, it is a sign, or representamen.

1895 | Short Logic: Chapter I. Of Reasoning in General | EP 2:13

A sign is a thing which serves to convey knowledge of some other thing, which it is said to stand for or represent. This thing is called the object of the sign; the idea in the mind that the sign excites, which is a mental sign of the same object, is called an interpretant of the sign.

1895 [c.] | On the Logic of Quantity, and especially of Infinity | MS [R] 16:12; PM 52

A sign, or representamen, involves a plural relation, for it may be defined as something in which an element of cognition is so embodied as to convey that cognition from the thought of the deliverer of the sign, in which that cognition was embodied, to the thought of the interpreter of the sign, in which that cognition is to be embodied.

1897 [c.] | On Signs [R] | CP 2.228

A sign, or representamen, is something which stands to somebody for something in some respect or capacity. It addresses somebody, that is, creates in the mind of that person an equivalent sign, or perhaps a more developed sign. That sign which it creates I call the interpretant of the first sign. The sign stands for something, its object. It stands for that object, not in all respects, but in reference to a sort of idea, which I have sometimes called the ground of the representamen. “Idea” is here to be understood in a sort of Platonic sense, very familiar in everyday talk; I mean in that sense in which we say that one man catches another man’s idea, in which we say that when a man recalls what he was thinking of at some previous time, he recalls the same idea, and in which when a man continues to think anything, say for a tenth of a second, in so far as the thought continues to agree with itself during that time, that is to have a like content, it is the same idea, and is not at each instant of the interval a new idea.

1899-1900 [c.] | Notes on Topical Geometry | MS [R] 142:3

A sign is a thing which is a representative, or deputy, of another thing for the purpose of affecting mind.

1901-1902 [c.] | Definitions for Baldwin's Dictionary [R] | MS [R] 1147

A representamen, or sign, is anything (not necessarily real) which stands at once in a relation of correspondence to a second third, its object, and to another possible representamen, its interpretant, which it determines to correspondence with the same object. It thus involves the idea of a possible endless series.

1901-1902 [c.] | Definitions for Baldwin's Dictionary [R] | MS [R] 1147

A representamen, or sign, is anything which stands, in any respect, at once in a relation of correspondence to a correlate, called its object[,] and to another correlate, its interpretant. which is a possible representamen determined by the first and referring to the same object. The idea of a representamen thus essentially involves the idea of an endless series.

1902 | Carnegie Institution Correspondence | NEM 4:54

A sign is something, A, which brings something, B, its interpretant sign, determined or created by it, into the same sort of correspondence (or a lower implied sort) with something, C, its object, as that in which itself stands to C.

1902 | Carnegie Institution Correspondence | NEM 4:20-1

a sign is something, A, which brings something, B, its interpretant sign determined or created by it, into the same sort of correspondence with something, C, its object, as that in which itself stands to C.

1902 | Minute Logic: Chapter I. Intended Characters of this Treatise | MS [R] 425:116

The categories directly point out that anything may be regarded, first, in the aspect of a simple Quale; secondly, as in Relation to other things; and thirdly, as a Sign, that is as referring to an object in virtue of determining an interpreting sign, which [I] call its interpretant[,] to refer to the object in the same way.

1902 [c.] | Reason's Rules | MS [R] 599:28-36

What is a sign? It is anything which in any way represents an object. This statement leaves us the difficulty of saying what “representing” is. Yet it affords help by pointing out that every sign refers to an object.


A sign does not function as a sign unless it is understood as a sign. It is impossible, in the present state of knowledge, to say, at once fully an precisely, and with a satisfactory approach to certitude, what it is to understand a sign. Consciousness is requisite for reasoning; and reasoning is required for the highest grade of understanding of the most perfect signs; but in view of the facts adduced by Von Hartmann and others concerning Unconscious Mind, it does not seem that consciousness can be considered as essential to the understanding of a sign. But what is indispensible is that there should be an interpretation of the sign; that is that the sign should, actually or virtually, bring about a determination of a sign by the same object of which it itself is a sign. This interpreting sign, like every sign, only functions as a sign so far as it again is interpreted, that is, actually or virtually, determines a sign of the same object of which it is itself a sign. Thus there is a virtual endless series of signs when a sign is understood; and a sign never understood can hardly be said to be a sign.


Is it not essential to a sign’s being a sign that its influence should never cease finally to live, as lending strength to a habit, law, or rule which is ready to produce action when occasion may arise, even although the truth of the sign (if it is a subject of truth or falsehood) be forever denied? [—] In this sense, every sign must be followed by an absolutely endless virtual succession of interpretant signs, or else not be in very truth a sign.

In the light of these considerations it is easy to see that the object of a sign, that to which it, virtually at least, professes to be applicable, can itself only be a sign

1902 [c.] | Reason's Rules | MS [R] 599:38

A sign is something which in some measure and in some respect makes its interpretant the sign of that of which it is itself the sign. [—] [A] sign which merely represents itself to itself is nothing else but that thing itself. The two infinite series, the one back toward the object, the other forward toward the interpretant, in this case collapse into an immediate present. The type of a sign is memory, which takes up the deliverance of past memory and delivers a portion of it to future memory.

1903 | C.S.P.'s Lowell Lectures of 1903 2nd Draught of 3rd Lecture | MS [R] 462:74

a sign is a thing related to an object and determining in the interpreter an interpreting sign of the same object. It involves the relation between sign, interpreting sign, and object.

1903 | Lowell Lectures on Some Topics of Logic Bearing on Questions Now Vexed. Part 1 of 3rd draught of 3rd Lecture | MS [R] 464:54; CP 1.346

a sign is something, A, which denotes some fact or object, B, to some interpretant thought, C.

1903 [c.] | On the Logical Nature of the Proposition | MS [R] 792:2

A sign is an object capable of determining in a mind a cognition of an object, called the object of the sign. A sign is a species under the genus representamen. A representamen is an object, A, in such a triadic relation to an object, B, for an object, C, (the italicized prepositions merely indicating a difference between the dyadic relation of A to B, and that of A to C) that A is fit to create C by the determination of something, so that C shall be in the same triadic relation to A, and thereby (such is the peculiar nature of this triadic relation) to B, for some third object, C’, determinable in the same manner, and so on ad infinitum.

1903 [c.] | P of L | MS [R] 800:3

A sign is a species under the genus representamen, the definition of which says nothing about a mind. A representamen is an object A, in such a triadic relation to an object, B, for an object C (the italicized prepositions merely indicating a difference between the relations) that it is fit to determine, C, to being in a similar triadic relation to A, and thereby (owing to the peculiar nature of this type of relation,) necessarily to B, for some third object, C’, determined in like manner, and so on ad infinitum.

1904 | A Brief Intellectual Autobiography by Charles Sanders Peirce | Peirce, 1983, p. 73; MS [R] L107:25

A sign is anything, A, in a relation, r, to something, B, its object, this relation, r, consisting in fitness to determine something so as to produce something, C, the interpretant of the sign, which shall be in the relation r to B, or at least in some analogous relation. Thus, the sign involves the idea of a possible endless series of interpretations. In what relation this entire series, taken as a whole, stands to the object, B, depends upon circumstances.

1904 | A Brief Intellectual Autobiography by Charles Sanders Peirce | Peirce, 1983, p. 77; MS [R] L107

Every sign is in a triadic relation to an object and to an interpretant, which is brought by the sign into a relation to the object similar to the sign’s relation to the same object. But it is necessary to distinguish between the object as it is represented by the sign and the object as it is in itself. It is also necessary to distinguish between 1st, the interpretant as it is intended to be determined by the sign, 2nd, the interpretant as it is related to the object, and 3rd, the interpretant as it is irrespective of the peculiarities of the sign and the object.

1904 | Foundations of Mathematics [R] | MS [R] 10:1

A sign in some sense corresponds to an object and also determines an interpretant sign, or is capable of doing so. Although it is not necessary that any person should originate the sign or that any person should interpret it, yet it will contribute to perspicuity to use language as if such were the case, and to speak of the utterer and the interpreter.

1904 | Firstness, Secondness, Thirdness, and the Reducibility of Fourthness [R] | MS [R] 914:5-6

The most characteristic form of thirdness is that of a sign; and it is shown that every cognition is of the nature of a sign. Every sign has an object, which may be regarded either as it is immediately represented in the sign to be [or] as it is in it own firstness. It is equally essential to the function of a sign that it should determine an Interpretant, or second correlate related to the object of the sign as the sign is itself related to that object; and this interpretant may be regarded as the sign represents it to be, as it is in its pure secondness to the object, and as it is in its own firstness. Upon these considerations are founded six trichotomic divisions of signs…

1904 [c.] | Draft of Nichols Review [C] | CP 8.191

“Representation” and “sign” are synonyms. The whole purpose of a sign is that it shall be interpreted in another sign; and its whole purport lies in the special character which it imparts to that interpretation. When a sign determines an interpretation of itself in another sign, it produces an effect external to itself, a physical effect, though the sign producing the effect may itself be not an existent object but merely a type. It produces this effect, not in this or that metaphysical sense, but in an indisputable sense.

1904.10.12 | Letters to Lady Welby | SS 31-2; CP 8.332

A sign mediates between the interpretant sign and its object. Taking sign in its broadest sense, its interpretant is not necessarily a sign. [—] A sign […] is an object which is in relation to its object on the one hand and to an interpretant on the other in such a way as to bring the interpretant into a relation to the object corresponding to its own relation to the object. I might say ‘similar to its own’ for a correspondence consists in a similarity; but perhaps correspondence is narrower.

1905 | Adirondack Summer School Lectures | MS [R] 1334:51-52

A sign is something which is in a triadic relation to two things being a sign of a object for an interprete. Its relation to its object is such as to determine the sign while producing little or no change in the object. As we usually say, the object is agent, the sign patient. There must actually be an object; at least, the sign must actually be affected by an object. But is is not essential that it should be more than fit to have an interprete. In order that the sign may actually function as a sign it must have an interprete but it is not essential that it should so function. It may suffice that it is fit so to function. Toward its interprete the sign is agent, the interprete patient. That is the sign essentially affects the interprete without being much affected itself. The relation of the sign to its object may be only dyadic, though in the case of symbols it is triadic. But the relation of the sign to its interprete is essentially triadic and consists in determining the interprete to a relation to the object corresponding to the relation of the sign itself to that object. In fact the interprete usually becomes itself a sign of the object for a possible interprete.

1905 | Notes on Portions of Hume's "Treatise on Human Nature" | MS [R] 939:42-4

It is difficult to define a sign in general. It is something which is in such a relation to an object that it determines, or might determine, another sign of the same object. This is true but considered as a definition it would involve a vicious circle, since it does not say what is meant by the interpretant being a “sign” of the same object. However, this much is clear; that a sign has essentially two correlates, its Object and its possible Interpretant sign. Of these three, Sign, Object, Interpretant, the Sign as being the very thing under consideration is Monadic, the Object is Dyadic, and the Interpretant is Triadic. We therefore look to see, whether there be not two Objects and three Interpretants. There obviously are two Objects, the object as it is in itself (the Monadic Object), and the object as the sign represents it to be (the Dyadic Object). There are also three Interpretants; namely, 1st, the Interpretant considered as an independent sign of the Object, 2nd, the Interpretant as it is as a fact determined by the Sign to be, and 3rd the Interpretant as it is intended by, or is represented in, the Sign to be.

1905 | Letters to Mario Calderoni | MS [R] L67:28, 35

A sign cannot function at all without producing a physical effect. All our thoughts of every description are signs. A sign is triadic because it determines an interpretant sign of the same object to which it refers itself. A sign is thus a sign of an object, for an interpretant.


A sign is something which is Secundan to an Object and determines an Interpretant to be correspondingly Secundan to the same Object. But we can distinguish two Objects; the object as it is represented to be, and the object as it is. We can also distinguish three Interpretants; the Interpretant as it is in itself regardless of the sign, the Interpretant as it is actually caused by the sign, and the Interpretant as the sign represents it to be intended.

1905-07 [c.] | On the theory of Collections and Multitude | MS [R] 31:2

A sign, as such, involves the third category, in its reference to an interpretant. Its reference to an object is an affair of the second category. Its reference to a meaning is specially a first category concern.

1905.07.07 | The Logic Notebook | MS [R] 339:247r

A sign is a Priman which is Secundan to an Object and is Tertian in determining an Interpretant into Secundanity to that Object.

1906 | The Basis of Pragmaticism | MS [R] 283:109-10

We can say, at once, that a sign must have these three characters: First, it must be a recognizable object in itself. Secondly, it must be determined to correspond, according to some principle, and by some species of causation, with something else, called its Object. In a word, whether physically, rationally, or otherwise, directly or indirectly, its Object, as agent, acts upon the sign, as patient. [—] But thirdly, the Sign, in its turn, acts upon the Interpreter-mind, or the quasi-mind corresponding thereto, and produces the Interpretant; and this action is essentially relative to the Object.

1906 | The Basis of Pragmaticism | EP 2:390-1

A sign is plainly a species of medium of communication, and medium of communication is a species of medium, and a medium is a species of third. [—]

A medium of communication is something, A, which being acted upon by something else, N, in its turn acts upon something, I, in a manner involving its determination by N, so that I shall thereby, through A and only through A, be acted upon by N.

1906 [c.] | On the System of Existential Graphs Considered as an Instrument for the Investigation of Logic | MS [R] 499

…a sign is a something which is on the one hand caused or otherwise determined by something else which is not utterly and altogether unreal, – this something else being the object of the sign. [—] But a sign is not only on the one hand determined by a more or less real object but on the other hand it determines something, – which I call its interpretant, – to be through it determined as it is by the object of the sign. The interpretants of the signs with which logic chiefly has to do are themselves signs. For every cognition is a sign as Leibniz and other nominalists have sufficiently shown and all deliberate meditation is of the nature of a dialogue as Plato represented it to be. But it is important to recognize that there are signs whose interpretants are not ipso facto signs. Such is the command of a captain of infantry “Ground arms!” [—]

The object is the sign’s determinant; the interpretant is the determinand of the sign and through the sign of the object likewise.

1906 [c.] | On Signs [R] | MS [R] 793:1; EP 2:544

For the purposes of this inquiry a Sign may be defined as a Medium for the communication of a Form. It is not logically necessary that anything possessing consciousness. that is, feeling of the peculiar common quality of all our feeling should be concerned. But it is necessary that there should be two, if not three quasi-minds, meaning things capable of varied determination as to forms of the kind communicated.

As a medium, the Sign is essentially in a triadic relation, to its Object which determines it, and to its Interpretant which it determines. In its relation to the Object, the Sign is passive; that is to say, its correspondence to the Object is brought about by an effect upon the Sign, the Object remaining unaffected. On the other hand, in its relation to the Interpretant the Sign is active, determining the Interpretant without being itself thereby affected.

1906.01.30 | The Logic Notebook | MS [R] 339:271r

A sign is a species of medium of communication.

The object, O, determines the sign, S, and S determines the Interpreting sign, I, to being determined by O through S.

1907 | Pragmatism | MS [R] 318:38

Premising that by intelligence I shall mean the character common to intelligent feelings, – such as those evoked by listening to a piece of concerted music, – intelligent actions, – though they rise no higher than a horse’s ordinary responses to even a driver’s touch, – and intelligent thought, I will suggest that a sign is anything which being intelligently determined by an Object in its turn intelligently determines an Interpretant, which thus becomes mediately determined by the Object.

1907 | Pragmatism | MS [R] 318:18-9

A sign is whatever there may be whose intent is to mediate between an utterer of it and an interpreter of it, both being repositories of thought, or quasi-minds, by conveying a meaning from the former to the latter. We may say that the sign is moulded to the meaning in the quasi-mind that utters it, where it was, virtually at least, (i.e. if not in fact, yet the moulding of the sign took place as if it had been there,) already an ingredient of thought. But thought being itself a sign the meaning must have been conveyed to that quasi-mind, from some anterior utterer of the thought, of which the utterer of the moulded sign had been the interpreter. The meaning of the moulded sign being conveyed to its interpreter, became the meaning of a thought in that quasi-mind; and as there conveyed in a thought-sign required an interpreter, the interpreter of the moulded sign becoming the utterer of this new thought-sign.

Enough of the italics! The next step toward our definition is the consideration that a chain of signs that conveys a given meaning can, in many ways, at any rate, be neither beginningless nor endless. Still, it must be of a mental nature. There must then be some other mental element than a sign that can endow a sign with a meaning: and some one upon which the meaning can be ultimately expended.

1907 | Pragmatism | MS [R] 318:13-4

any sign, of whatsoever kind, professes to mediate between an Object, on the one hand, that to which it applies, and which is thus in a sense the cause of the sign, and, on the other hand, a Meaning, or to use a preferable technical term, an Interpretant, that which the sign expresses, the result which it produces in its capacity as sign.

1907 | Pragmatism | MS [R] 318:19

Remember my definition of a “sign,” upon which I have a right to insist as that of a new term of logic, just as a zoölogist has a right to define “fish” so as to exclude star-fishes. jelly-fishes, shell-fish, and whales. A “sign,”, I say, shall be understood as anything which represents itself to convey an influence from an Object, so that this may intelligently determine a “meaning,” or interpretant.

1907 | Pragmatism | MS [R] 318:11-2

any sign, of whatever kind, mediates between an object to some sort of conformity with which it is moulded, and which thus determines it, and an effect which it is intended to produce, and which it represents to be the outcome of the object. These two correlates of the sign have to be carefully distinguished. The former is called the object of the sign; the latter is the “meaning,” or, as I usually term it, the “interpretant” of the sign.

1907 | Pragmatism | MS [R] 318:14-5

the essential nature of a sign is that it mediates between its Object which is supposed to determine it and to be, in some sense, the cause of it, and its Meaning, or, as I prefer to say, in order to avoid certain ambiguities, its Interpretant, which is determined by the sign; and is, in a sense, the effect of it; and which the sign represents to flow as an influence, from the Object. [—] So far, so good: the Object, the determinant of the Sign, and the Meaning, or Interpretant, that which the sign, as such, determines, its effect.

1907 | Pragmatism | EP 2:410

I am now prepared to risk an attempt at defining a sign, – since in scientific inquiry, as in other enterprises, the maxim holds, Nothing hazard, nothing gain. I will say that a sign is anything, of whatsoever mode of being, which mediates between an object and an interpretant; since it is both determined by the object relatively to the interpretant, and determines the interpretant in reference to the object, in such wise as to cause the interpretant to be determined by the object through the mediation of this “sign.”

1907 [c.] | Pragmatism | MS [R] 321:15-6, 19

any sign, of whatsoever kind, mediates between an Object to some sort of conformity with which it is moulded, and by which it is thus determined, and an effect which the sign is intended to bring about, and which it represents to be the outcome of the object’s influence upon it. It is of the first importance in such studies as these that the two correlates of the sign should be clearly distinguished: the Object by which the sign is determined and the Meaning, or as I usually call it, the Interpretant, which is determined by the sign, and through it by the object. The meaning may itself be a sign, a concept, for example, as may also the object. But everybody who looks out of his eyes well knows that thoughts bring about tremendous physical effects, that are not, as such, signs. Feelings, too, may be excited by signs without thereby and therein being themselves signs. [—] …it must not be forgotten that every sign is besides just an object like any other, and it may be two very different signs at once.

1908 | Letters to Lady Welby | SS 80-81

I define a Sign as anything which is so determined by something else, called its Object, and so determines an effect upon a person, which effect I call its Interpretant, that the latter is thereby mediately determined by the former. My insertion of “upon a person” is a sop to Cerberus, because I despair of making my own broader conception understood.

1908.12 | Letters to Lady Welby | CP 8.343

I define a Sign as anything which on the one hand is so determined by an Object and on the other hand so determines an idea in a person’s mind, that this latter determination, which I term the Interpretant of the sign, is thereby mediately determined by that Object. A sign, therefore, has a triadic relation to its Object and to its Interpretant.

1909 | Letters to William James | EP 2:492

A Sign is a Cognizable that, on the one hand, is so determined (i.e., specialized, bestimmt) by something other than itself, called its Object […], while, on the other hand, it so determines some actual or potential Mind, the determination whereof I term the Interpretant created by the Sign, that that Interpreting Mind is therein determined mediately by the Object.

1909 | Meaning Preface | MS [R] 637:31-32

…the word Sign will be used throughout the volume to denote an Object perceptible, or only imaginable, or even unimaginable in one sense, – for the word ‘fast’, which is a Sign, is not imaginable, since it is not this word itself that can be set down on paper or pronounced, but only an instance of it and since it is the very same word when it is written as it is when it is pronounced, but is one word when it means ‘rapidly’ and quite another when it means ‘immovable,’ and a third when it refers to abstinence. But in order that anything should be a Sign, it must “represent,” as we say, something else, called its Object, although the condition that a Sign must be other than its Object is perhaps arbitrary, since, if we insist upon it we must make an exception in the case of a Sign that is a part of a Sign. [—]

It is not only essential to a Sign that it shall represent an Object, but it is at least as much so that it should be capable of Interpretation by a mind; and until it be so interpreted it does not function as a Sign. That is to say, the Sign must act upon the mind of the Interpreter in such a way that the latter shall be affected substantially as if by the Object (for so far as the Sign is deceptive it is not a Sign of its Object;) though the Interpreter will pe[r]ceive that it is the Sign and not the Object itself that directly affects him.

1909 | Meaning Preface | MS [R] 637:36

It is not only essential to a Sign that it should represent, i.e. stand in place of or for, an Object, but, if possible, still more so that it should be capable of Interpretation by or through a mind, into which it implants a germ which, on development, will affect the conduct of the person to whom that mind appertains; and not until this effect, which throughout this volume will be called the Interpretant of the Sign, is brought about will the sign function as the Sign greek.

1909 | Essays on Meaning. Preface | MS [R] 640:7-8

A Sign […] is anything which represents something else, its Object, to any mind that can Interpret it so. More explicitly, the Sign is something that appears, in place of its Object, which does not appear for itself, (at least, not in the respect in which the Sign appears;) so that the Sign […] is, as it were, the species, or appearance, virtually or figuratively speaking, emanating from the Object, and capable of producing upon an intelligent being an effect that will […] be called the Interpretant of the Sign, and effect which is recognized as due, in some sense[,] to the Object; and it is in producing the Interpretant so that it is referred to the Object, that the Sign fulfills the function its fitness for which constitutes it a “Sign.”

1909.10.28 | The Prescott Book | MS [R] 277

A Sign is anything which represents something else (so far as it is complete), and if it represents itself it is as a part of another sign which represents something other than itself, and it represents itself in other circumstances, in other connections. [—]

Either a Sign is to be defined as something which truly represents something else or else as something which professes to represent something.

1909.12.25 | Letters to William James | EP 2:500

I start by defining what I mean by a Sign. It is something determined by something else, its Object, and itself influencing some person in such a way that that person becomes thereby mediately influenced or determined in some respect by that Object.

1910 | Essays | MS [R] 654:7

By a sign I mean anything whatever, real or fictile, which is capable of a sensible form, is applicable to something other than itself, that is already known, and that is capable of being so interpreted in another sign which I call its Interpretant as to communicate something that may not have been previously known about its Object. There is thus a triadic relation between any Sign, an Object, and an Interpretant.

1910 | The Art of Reasoning Elucidated | MS [R] 678:23

we apply this word “sign” to everything recognizable whether to our outward senses or to our inward feeling and imagination, provided only it calls up some feeling, effort, or thought

1910 [c.] | Letters to Paul Carus | ILS 284

A sign in general is 1st something Real, that is 2nd applicable to an object different from itself and already known to the person to whom it is a sign, and 3rd is capable of interpretation in the mind of that person, so that it will (or would if accepted as veracious sign) have some effect upon him of a kind it was calculated or fit to have.

nd | Miscellaneous Fragments [R] | MS [R] S104

A sign is anything, A[,] which is in a genuine triadic relation to a so-called ‘Object,’ B, for a so[-]called ‘Interpretant,’, C.