Vocabulary is the most unstable element of a language as it is undergoing constant changes both in form and content. Comparatively, the content is even more unstable than the form This chapter will deal with the major patterns that changes in meaning follow and the causes of changes English lexicology(Ill)English lexicology (III) 3  Vocabulary is the most unstable element of a language as it is undergoing constant changes both in form and content. Comparatively, the content is even more unstable than the form.  This chapter will deal with the major patterns that changes in meaning follow and the causes of changes