Introduction

Abstract

Let us take a look at something. Let us see what can be found in something that could be anything, for instance, something like an X. What is it? Is it a sign? Yes, at least it can be a sign. The moment we decide that it means something, it becomes a sign. The easiest way to make the X mean something is to put it in some sort of context, for instance, a conventional sign system: the Greek or the Latin alphabets, the sign systems of mathematics or logic, or some other more or less settled scheme. We know what to do with X in the word ‘mix’ and we know that X, in an equation such as ‘3 + X = 5’, means the unknown number.