There are many general truths with regard to signs which hold good for all signs whatever

Charles S. Pierce on the Logic of Signs 
. "Now there are many general truths with regard to signs which hold good for all signs whatever, of necessity; being involved in the essential nature of signs. The origin of these principles is undoubtedly the nature of the mind. But they are involved in so much of what is true of the mind as is implied in our capability of reasoning at all and which may therefore be said to be implicitly taken for granted by all men, that is, to be deducible from what everybody agrees to and must agree to before we can begin any discussion whatever in a rational way, and which is thus taken out of the special domain of psychology and made the common property of science. These principles might be evolved from a study of the mind and of thought, but they can also be reached by the simple consideration of any signs we please. Now the latter mode of studying them is much the easiest, because the examination of external signs is one of the most simple researches which we can undertake, and least susceptible to error, while the study of the mind is one of the most difficult and doubtful. We shall therefore proceed in the remainder of this part of the work to compare signs, and generalize our results, being guided in doing so by a certain feeling of the necessity that this or that must be true, such as is felt in mathematics the origin of which necessity clearly is, in this case at least, that the principles are involved in the postulate, that the mind is so constituted as to investigate."
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