Lexical field theory, or word-field theory, was introduced on March 12, 1931 by the German linguist Jost Trier. He argued that words acquired their meaning through their relationships to other words within the same word-field. An extension of the sense of one word narrows the meaning of neighboring words, with the words in a field fitting neatly together like a mosaic. If a single word undergoes a semantic change, then the whole structure of the lexical field changes. The lexical field is often used in English to describe terms further with use of different words.