公益广告在告知大众重要的社会问题，并激发他们采取积极行动方面发挥非常重要的作用。基于系统功能语法的言语角色，本文对从美国较有影响力杂志中，随意选取17篇公益广告进行言语角色分析。研究发现公益广告语篇的两个言语角色：给予信息和求取积极行动。给予信息基本上都是通过完整陈述句来表达的，然而，省略陈述句和反意陈述句同样可以实现这一言语功能。省略句的使用显示广告者试图营造与读者的亲密氛围从而缩短两者之间的距离。求取行为主要是通过祈使句，然而疑问句和陈述句同样可以实现这一功能。公益广告语篇中，祈使句的频繁使用显示广告者更高的社会地位；同时，公益广告语篇中还有一些对抗反应和问题答案。这个研究表明反驳陈述和问题答案都是广告说服目的的产物。

关键词：公益广告、言语角色、言语反应

Public service advertising texts play important role in informing the public of serious social problems and stimulating them to take positive actions. Base on the speech role theory of system-functional grammar, this essay analyzes the speech role of 17 public service advertising texts chosen from the American famous magazines. Two speech roles in public service advertising texts are giving: information and demanding positive action. Giving information is primarily expressed by full declaratives, however, elliptical and tagged declaratives also realize this speech function. The use of elliptical declaratives indicates that the advertiser tries to create an intimate atmosphere with the reader and narrow the distance between them. Demanding action is dominantly realized by imperatives, while interrogatives and declaratives are also chosen to fulfill this function. The frequent use of imperatives indicates the higher social status of the advertiser in public service advertising texts. In addition, there are confronting responses followed by some statements and answers provided for the questions in public service advertising texts. The study shows that contradiction to the statement and the answer to the question both serve persuasive effects of advertising.

Keywords: Public Service Advertisement, Speech Role, Speech Responses