Pierce defines these three topics as the basic elements of semiotics. The sign can be defined simply as anything that can be interpreted. Signs are classified into three distinct types: icon, index, and symbols. Each type is defined by specific characteristics, which define its meaning for the sign. An icon is a sign that is connected to an entity through qualitative characteristics, such as appearance, sound, touch, taste, and smell. An example of an icon is a map, the map is an icon because it shares the same qualities as the territory represented by the map. An index is the denotation of an entity physically connected to or affected by a sign. An example of an index is smoke signals, smoke signals are a direct indication of the fire, the conclusion that smoke is a physical consequence of the fire. The last type is the symbol, a symbol is a sign without any qualitative or physical connection to an entity. If they are symbols, they have no direct qualitative or physical connection to the transmitting entity. Sign types are a key tool in ensuring that intended meanings are unambiguously understood by both the author and the reader. An object can be anything questionable about the subject of a sign, such as discussing what that "something" was said about it