Footnote at pp. 126-127; As cited in: Adam Schaff (1962). Introduction to semantics, p. 313-314 
The Origins and Prehistory of Language, 1956
                                    
“Language is a purely human and non-instinctive method of communicating ideas, emotions and desires by means of a system of voluntarily produced symbols.”
            As cited in: Geza Revesz, The Origins and Prehistory of Language, London 1956. footnote pp. 126-127; As cited in: Adam Schaff (1962). Introduction to semantics, p. 313-314 
Language (1921)
        
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Edward Sapir 10
American linguist and anthropologist 1884–1939Related quotes
“Language is a system of conventional signs that can be voluntarily produced at any time.”
Hermann Ebbinghaus, quoted in: Geza Revesz, The Origins and Prehistory of Language, London 1956. footnote p. 126
Source: The Principles of Art (1938), p. 268
Source: The Principles of Art (1938), p. 269
Source: 1930s, "Protocol Statements" (1932), p. 91
Source: Attributed from posthumous publications, Dialogues of Alfred North Whitehead (1954), Ch. 29, June 10, 1943.
                                        
                                        Selected Writings—Poetry and Criticism. (1964). 
Other Quotes
                                    
Source: Textual politics: Discourse and social dynamics, 1995, p. 6