 What are strings made of? There are two possible answers to this question. First, strings are truly fundamental—they are “atoms,” uncuttable constituents. … As the absolute smallest constituents of anything and everything, they represent the end of the line … in the numerous layers of substructure in the microscopic world. From this perspective, even though strings have spatial extent, the question of their composition is without any content. Were strings to be made of something smaller they would not be fundamental. Instead, whatever strings were composed of would immediately displace them and lay claim to being an even more basic constituent of the universe … [A] string is simply a string—as there is nothing more fundamental, it can't be described as being composed of any other substance. (1999: 141–2)