When most people think of language variation, they think of geographic variation. However, variation can be caused by any type of separation that causes one group of speakers to have less contact with another group of speakers. Hence, differences exist in the speech of different geographic areas, social classes, ethnic groups, professions, age groups, and sexes. A dialect can be defined as any variety of language spoken by a group of people. Therefore, linguists can talk about geographic dialects, social dialects, ethnic dialects, etc. The term standard dialect has historically referred to that dialect that has, because of political and social factors, the most prestige. The standard dialect is not linguistically superior to other dialects; it is possible to communicate clearly in any dialect. An individual knows many dialects and varies his/her speech according to the audience. In the past several years, many linguists have stopped using the term dialect since it often has a negative connotation for others. Instead, they use the term variety. In the newer terminology, standard dialect has been replaced with prestige variety.
Each speaker is also able to use different styles depending upon the subject matter, the situation, and the medium. Sometimes, styles are described as a continuum, as follows (from Joos The Five Clocks):
FROZEN used in pledges, prayers, etc.; no listener participation Example: "With this ring I thee wed"
FORMAL used in speeches; little listener participation Example: "Ask not what your country can do for you"
CONSULTATIVE used in work situations polite interruptions are possible Example: "I believe this report accurately reflects our present situation"
CASUAL used among friends; interruptions frequent; many shared assumptions Example: "Do you have anything to wear to the party?"