This paper explains at least some of the major problems related to the subject indexing process and proposes a new approach to understanding the process, which is ordinarily described as a process that takes a number of steps. The subject is first determined, then it is described in a few sentences and, lastly, the description of the subject is converted into the indexing language. It is argued that this typical approach characteristically lacks an understanding of what the central nature of the process is. Indexing is not a neutral and objective representation of a document's subject matter but the representation of an interpretation of a document for future use. Semiotics is offered here as a framework for understanding the 'interpretative' nature of the subject indexing process. By placing this process within Peirce's semiotic framework of ideas and terminology, a more detailed description of the process is offered which shows that the uncertainty generally associated with this process is created by the fact that the indexer goes through a number of steps and creates the subject matter of the document during this process. The creation of the subject matter is based on the indexer's social and cultural context. The paper offers an explanation of what occurs in the indexing process and suggests that there is only little certainty to its result.