There are some reasons that have been proposed for language change. First is the anatomy and ethnic character. Anatomical differences were often assumed to be related to cultural differences. Cultural differences between people caused language change especially sound change. The second is climate and geography. They influence language change because the perception that a harsh physical environment could produce harsh sounds in language. The ‘harshness’ here is the phonetic harshness like guttural sounds and complex consonant clusters. The third is substratum. The substratum theory says that if people migrate into an area and their language is acquired by the original inhabitants of the area, then any changes in language can be put down to the influence of the original language. However, there is a weakness of the substratum explanation of language change. That is the influence can be neither proved nor disapproved.
The fourth is local identification, Don Laycock, a linguist, said that language may change simply to allow their speakers to distinguish things about their speech that are different from the speech of other people. The language changes can be deliberated and planned when language is used as a tool for local identification. The fifth is functional need. Language changes because a particular language must change in order to meet new demands that speakers place upon it. As the functional need of language change, some aspects of the language may be lost while others may be added. The sixth is simplification. Simplification happens when we are making words shorter and we need to exert less physical effort to produce them. However, there are several problems that associated with the language change explanation. The seventh is structural pressure. The concept of structural pressure is that languages operate in terms of systems, if systems becomes unbalance or have ‘gap’ then a change is likely to take place as a way of filling that gap. The last one is the social upheaval. The theory of upheaval is there is less likely to be direct control of children by parents, so there would be less pressure of correction, thereby allowing innovations to go through uncorrected by the older generation. That is all about the reason of language changes that I have gotten in this chapter, perhaps there are other reasons that not mention in this chapter.
Crowley, Terry. 1997. An Introduction to Historical Linguistics. Oxford University Press: Australia.