On the other hand Le Bon's theory of crowd refers to the people who are the same in thinking and gradually get together in a same place; ex. bookworms used to stay in the library. Simmel's notions of alienation and individualization give ways to prove us and understand the urban identity, that the people in urban areas are said to be divided for which, people are separating due to their environments changes, its either they can't adjust or they don't want to adjust with it. For instance, on a public library, you will see some people who are separated from the others, some are with their perspective groups, doing different things on their own. Here you see that people with the same nature and thinking are together while others are alienatedly separated from them, here you will see individualization, an individual subjectivity.
Avant Garde is a French military term "vanguard" which goal is to advanced and experiment movements in the arts. They comment for changes in the form of art as well as an effort on the part of tastes. The writers and artists of the American avant garde generally manifested itself abroad, which are to release themselves from the bondage of establishments.