Writing is a medium of human communication that involves the representation of a language with written symbols. Writing systems are not themselves human languages; they are means of rendering a language into a form that can be reconstructed by other humans separated by time and/or space. While not all languages utilize a writing system, those with systems of inscriptions can complement and extend capacities of spoken language by enabling the creation of durable forms of speech that can be transmitted across space and stored over time. It has also been observed that the activity of writing itself can have knowledge-transforming effects, since it allows humans to externalize their thinking in forms that are easier to reflect on, elaborate, reconsider, and revise. Writing relies on many of the same semantic structures as the speech it represents, such as lexicon and syntax, with the added dependency of a system of symbols to represent that language's phonology and morphology. The result of the activity of writing is called a text, and the interpreter or activator of this text is called a reader.