There are some heated discussions lately on the use of foul language by Hong Kong Legislative Councilors during council discussions. This incident reminds me a book about the linguistic history of the English Language. This book, among other things, talks about semantic change in English words and points out that the meaning of words are very flexible and fluid, although dictionaries purport to give us the correct meaning of a word. Also, semantic change may link to cultural, social and political changes. In total, the book lists out seven types of semantic changes, namely: i) generalization and specialization ii) pejoration and amelioration iii) weakening and strengthening iv) figurative shifts v) invited inferences vi) cultural change, and vii) social change. Of these changes, social change include changes that come from below in the form of slang. According to the book, slang is " the specialized language of any cohesive group (such as a class, an age group, a professional group, etc.", it often gives a new meaning to an existing word, usually it is ephemeral. More information of the book: Laurel Brinton & Leslie Arnovick, The English Language: a Linguistic History (Oxford University Press, 2006). In my Thesaurus I find the the word "slang" has synonyms such as colloquialism, regionalism, vulgarism, and barbarism etc. As for "foul", it has synonyms that include obscene, vulgar, coarse and indecent etc. As for "vulgar", its synonyms include: ignorant, uncultured, low-class, indecent, shameless, disgusting, obscene, lewd, pornographic etc. etc. I think these synonyms may help us figure out the true nature of foul language. To those who love using foul language, there is a piece of advice: you are what you speak.