 Martinet's concept is similar to Zipf's principle of least effort; although the idea had been discussed by various linguists in the late 19th and early 20th century.Some key adaptations of functional explanation are found in the study of information structure.Based on earlier linguists' work, Prague Circle linguists Vilém Mathesius, Jan Firbas and others elaborated the concept of theme–rheme relations (topic and comment) to study pragmatic concepts such as sentence focus, and givenness of information, to successfully explain word-order variation.