Assignments of topic characteristics are always made within a specific context, which may or may not be explicit. For example, if I (yet again) mention “tosca”, I should expect my readers to think of the opera by Puccini (or its principle character), because of the context that has been set by the examples used so far in this paper. For an audience of bakers, however, the name “tosca” has quite other and sweeter connotations: it denotes another topic altogether. Although we seldom notice it in everyday life, the problem of context is with us all the time. According to [Sowa 1984] a sentence is derived from six different kinds of information, four of which ( tense and modality; presupposition; focus; and emotional connotations) are in one way or another related to context. Humans are remarkably good at dealing with context. It is that ability that enables them to make sense of two such similar statements as John Smith to marry Mary Jones on the one hand, and Retired priest to marry Bruce Springsteen on the other, or to parse and interpret the two sentences Time flies like an arrow and Fruit flies like an apple.[9] Computers, however, are not yet that smart. Given two such simple statements as Tosca takes place in Rome and Tosca kills Scarpia, most of today's computers would not be able to infer which of the topics named “Tosca” was involved. In order to avoid this kind of problem, topic maps consider any assignment of a characteristic to a topic, be it a name, an occurrence or a role, to be valid within certain limits, which may or may not be specified explicitly. The limit of validity of such an assignment is called its scope. Scope is defined in terms of themes, and a theme is defined as “a member of the set of topics used to specify a scope”. In other words, a theme is a topic that is used to limit the validity of a set of assignments. Thus, the name “tosca” might be assigned to three different topics in scopes defined by the themes “opera”, “opera”+“character”, and “baking” respectively, thereby removing any ambiguity and reducing the chance of errors, for example when merging topic maps. In fact, the well-designed, consistent and imaginative use of scope in topic maps does much more than simply remove ambiguity. It can also aid navigation, for example by dynamically altering the view on a topic map based on the user profile and the way in which the map is used. For example, any user that declares a specific interest in opera (or a specific lack of interest in baking!) can have the various toscas ranked accordingly.