In the early 20th century Ferdinand de Saussure distinguished between the notions of langue and parole in his formulation of structural linguistics. According to him, parole is the specific utterance of speech, whereas langue refers to an abstract phenomenon that theoretically defines the principles and system of rules that govern a language. This distinction resembles the one made by Noam Chomsky between competence and performance, where competence is individual's ideal knowledge of a language, while performance is the specific way in which it is used. In classical Indian philosophy of language, the Sanskrit philosophers like Patanjali and Katyayana had distinguished between sphota (light) and dhvani (sound). In the late 20th century, French philosopher Jacques Derrida distinguished between the notions of speech and writing. Nomenclature Variation and Universality Lexicon The lexicon is a catalogue of words and terms that are stored in a speaker's mind.
Related: The problems with philosophy
• The Story of Human Language