When dealing with linguistic signs, evolution is inescapable. Thus, language's arbitrariness leads to modification and formation of new linguistic signs. This may not be the only truth or accepted fact but this is one truth about language- it is arbitrary. In defiance of its internal structure, we don't just say that it is always the heritage of the past experiences or preceding interactions, because time must also be checked or considered when talking about language. These social forces must always be associated with time. Since language perpetuates itself or continues to exist, we expect some changes in it. The need for making new languages is one of the reasons why language is considered as mutable. Through time, more words are actually constructed (Saussure, 1916). .
"One of the central "design features " of human language is that the relationship between the sound of a word and its meaning is arbitrary; given the sound of an unknown word, it is not possible to infer its meaning " (Christiansen, M. H., Kirby, S., Monaghan, P., & Shillock, R. C., n.d). Speaking of diachronic linguistics, everything that relates with the evolutionary side is diachronic. The principle of continuity tells us that time changes things. After a certain period of time, some modifications are noticeable. External linguistics does not actually affect the inner system of a language. Yet it helps add or coin more terms. Since language is arbitrary, it doesn't have the power to protect itself against social forces which can possibly shift the relationship between the signified and the signifier. As it is said, even though the inner system is immutable, still signifiers can be multiple (Saussure, 1916). Languages are arbitrary because the rules for combining signs in producing certain thoughts are different from one language to the other, and no set of rules can claim to be the "right one ". Different languages are said to have had different conventions, and these conventions can actually do change.