Reference
- Morris , C. 1938 . “ Foundations of the theory of signs ” . In International encyclopedia of unified science , Edited by: Neurath , O. , Carnap , R. and Morris , C. Vol. 1, no. 2 , 1 – 2 . Chicago : University of Chicago Press . (reprint in: Morris, C. 1971. Writings on the general theory of signs, Hague, The Netherlands: Mouton, 17)