Abstract: To dissolve problems in debates over the arbitrariness of linguistic signs, this paper attempts to elucidate Saussure's principle of arbitrariness by clarifying his philosophy of language.Based on Course in General Linguistics and Writings in General Linguistics, the study finds that 1) Saussure's philosophical approach to language is characterized by isolating it from reality and thus interpreting the meaning of its signs within language itself; 2) arbitrariness is thus the first principle governing the meaning relation between the signifier and the signified of a linguistic sign; 3) on this basis core concepts are gradually introduced and thereby a unique theory of meaning and an original theoretical system of general linguistics developed; 4) debaters' problems with Saussure's principle of arbitrariness occurred when they understood just its linguistic nature while neglecting its philosophical essence.