| In modern society, the right of freedom of speech as a basic human right has been widely accepted by various countries. There is a limit to free speech, and the freedom of speech is not protected by law when beyond the legal boundaries. United States, as a country with the most developed system of freedom of speech, through the Bill of Rights established the constitutional protection of freedom of speech as soon as it was founded, during the next two hundreds of years, Federal Supreme Court Justices continually given new connotation to free speech based on judicial precedents, and kept extending the boundaries of free speech, finally formed a distinctive constitutional protection system of freedom of speech. Therefore, for China to improve the constitutional protection of freedom of speech, to promote the construction of the legal government, and to push the implementation of constitution, it has an important referential significance to study the constitutional protection of the boundaries of freedom of speech in the United States.The first chapter primarily uses the historical research method, and introduces the theoretical basis and development situation of free speech in the United States. Points out that freedom of speech in America have two theories:individual freedom of free speech and political freedom of free speech. Based on the influence of two concepts and development of times, it has been formed a special justice criterion in the boundaries of freedom of speech and the constitutional protection. The contemporary development of freedom of speech in America, show a trend of diversity, the argument of traditional free speech has been replaced by new issue of freedom of speech. While dealing with the variety of new issues of freedom of speech, the stand of Federal Supreme Court Justices presents a situation of division. The second chapter adopts the method of classification research to study the boundaries of freedom of speech and the constitutional protection in the United States. According to the two basic theories of freedom of speech, it can be divided into public field and private field of freedom of speech, the degree and range is different in accordance with the different types of boundaries of freedom of speech and the constitutional protection. Thus, it covers the most of problems of freedom of speech in the United States, including inflammatory comment, symbolic speech, hate speech, obscene speech, defamatory statement, commercial speech, political campaign, finance reform, freedom of the press, etc. This chapter discusses the legal boundaries and constitutional protection of above-mentioned speeches. The third chapter mainly uses the comparative method of study, explores the enlightenment of the American constitutional protection model of the boundaries of freedom of speech to the protection of free speech in China. This chapter gives a comprehensive review on the pros and cons of the American model, based on Chinese situation and the status quo of the constitutional protection of freedom of speech, and puts forward proposals to improve the protection of freedom of speech. |