Charles S. Peirce
On the Nature of Signs
MS 214 (Robin 381): Writings 3, 66-68
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. What I mean will best be understood by illustration. A weathercock is a sign of the direction of the wind. It would not be so unless the wind made it turn round. There is to be such a physical connection between every sign and its object. Take a painted portrait. It is the sign of the person for whom it is intended. It is a sign of that person in virtue of its likeness to that person: but this is not enoughit cannot be said of any two things that are alike one is a sign of the other but the portrait is a sign of that person because it was painted after that person and represents him. The connection here is an indirect one. The appearance of the person made a certain impression upon the painter's mind and that acted to cause the painter to make such a picture as he did do so that the appearance of the portrait is really an effect of the appearance of the person for whom it was intended. The one caused the other through the medium of the painter's mind. Take any statement which is made concerning a matter of fact. It is caused or determined by the fact. The fact has been observed & the perception of the fact which was caused by it in its turn causes the statement to be made. Perhaps however the fact was not directly perceived. The statement may be a prediction. In that case it cannot be said that that which follows after has caused that which precedes it, the prediction, but if the event has been predicted it has been through some knowledge of its cause and this same cause which precedes the event also precedes some cognition of the mind which gave rise to the prediction so that there is a real causal connection between the sign and the thing signified although it does not consist in one's being the effect of the other but in both being the effect of the same cause. 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 lo 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. The idea itself has its material quality which is the feeling which there is in thinking. Thus the red and blue are different in the mere sensation. This difference in no way resembles the distinction which there is between those things in the outward world which are called red and those things which are called blue. These things differ only in the rapidity with which their particles vibrate. In order that the senses discriminate between the two cases it is necessary that there should be some difference in the sensation but it is entirely indifferent so far as the difference of sensation is concerned whether it be a shorter or a longer vibration which produces that peculiar sensation which red things do. Whatever looks red might look blue or vice versa and the representation would be equally true to the facts. Thus our mere sensations are only the material quality of our ideas considered as signs. Our ideas have also a causal connection with the things that they represent without which there would be no real knowledge. It is not so clear at first sight that our ideas resemble their signs in necessarily appealing to some mind. That appeal could amount to nothing except the production of certain other ideas in which the first one should be virtually reproduced and according to the ordinary conception of the mind when the idea has once reached consciousness the correlation is complete. Nevertheless I regard this as an error of a very important character.