A Literature Review of Linguistic Research in Public Service Announcements

. Unlike commercial advertisements, public service announcements (PSAs) are non-profit in nature and take the important social responsibility of providing moral and ethical education through the different channels of media. In recent years, linguistic studies of PSAs have become popular among scholars. In order to explore the trend of linguistic research on PSAs, this paper searched 34 Chinese pieces of literature on China National Knowledge Internet (CNKI), using “PSAs” and “linguistics” as keywords, finding that most of these scholars have explored the language of PSAs from the perspective of pragmatics, either comprehensively or in-depth, and the related research directions are becoming more and more innovative, showing a new trend of integrating different disciplines.


The Concept of Public Service Announcements and Linguistic Research
Public service announcement (henceforth, PSA), was defined as a form of advertising communication. With its special functions in education, it distinguishes itself from other profitable advertisements. It focuses on the public acceptance patterns, the channels of its distribution that might raise the number of mass addressees, and the role of the state in their production (Chubay, 2017). In other words, PSA is a non-profit means of social and popular propaganda, aiming to disseminate ideas that are in line with current social interests and ethics, either through official channels or through the power of public opinion. In today's rapidly advancing modern technology, the public's pursuit of a refined civilization is becoming more and more important after the satisfaction of material civilization, and therefore PSA plays an important role in enhancing the ideological awareness of the citizens and building a good social ethos.
The use of PSAs has a direct impact on the effectiveness and persuasiveness of the advertisements themselves. In recent years, more and more scholars have come to recognize this, and have conducted linguistic research on the language use of PSAs. The linguistic disciplines involved are complex, so a systematic review and consolidation of these disciplines will help readers understand the linguistic context of PSA from a linguistic perspective. A total of 34 Chinese articles were retrieved from the CNKI by searching the keywords "public service announcements" and "linguistics in public service announcements". Therefore, this study takes these 34 Chinese papers on the linguistic study of PSAs in the past fifteen years (2006-2021) as the research object. This paper uses the method of documentary analysis to explore the research results and trends during this period. Besides, this study also provides suggestions for future research directions so as to expand the research horizon of linguistics and provide references to design the language of PSAs language.

Speech Act Theory
Austin put forward the theory of speech act, which held that speech is action. Austin divided speech acts into three levels: locutionary act, that is, the act expressing literal meaning through phonology, vocabulary, and syntax; illocutionary act, means that the speaker expresses a certain intention or purpose through statements, requests, commitments, and other speech acts; perlocutionary act means that the speaker influences or changes the attitude, thought and behavior of the addressee through utterance. For example, Jiang (2017) classified different speech acts in the selfbuilt corpus of PSAs and showed the role and influence of speech acts on indirect persuasion strategies and the effectiveness of PSAs from the perspective of PSAs' issuers and audiences, respectively. Focusing on the tripartite of speech act theory, Li (2021) indicated the important role of speech acts in the effectiveness of PSAs and emphasized that issuers of PSAs need to focus on the conclusion of speech acts to be fully understood by the audiences. Wang (2011) used a self-built corpus to conduct an inductive analysis to provide a comprehensive account of PSAs from the perspective of pragmatics and analyzed the pragmatic features, strategies, and functions of PSAs with the help of speech act theory and pragmatic principles such as cooperation and politeness. Lan (2012) analyzed the embodiment of speech acts and conversational meanings in PSA phrases and the related guidelines from a pragmatic perspective. From the perspective of speech act theory, previous studies that focused on dynamic speech act perspective analysis were concentrating on the communication process between the PSAs and the advertising audience, which makes up for the deficiency of existing research.

Relevance Theory
According to Sperber & Wilson (2001), relevance is a generalization of what takes place in human communication. Human cognition is relevance-oriented which means that human attention and thought turn toward relevant information automatically. Relevance theory consists of cognitive principle and communicative principle. Using the relevance-adaptation theory, Cheng & Sun (2018) collected print PSAs in the form of images as a self-built corpus, and combined quantitative statistics to systematically analyze and classify the specific print PSAs on the topic of "Talking about civilization and making a new style" from both the issuers and audiences of PSAs. The analysis revealed the role of context, pictorial symbols, and adaptation theory on the PSA system. He found that the issuers of such PSAs used relevance-adaptation theory to enhance their acceptability and persuasiveness in both linguistic and pictorial modalities, and further explained the importance of their design and promotion to social culture. Wang (2016) also analyzed the use of metaphors in Chinese PSAs from the perspective of relevance theory and the stimulus-response model, showing the mechanism and characteristics of metaphors and revealing their pragmatic functions in PSAs. From the perspective of relevance theory, previous studies focused on the mechanism of PSA, finding that speakers design appropriate PSAs through various relevance assumptions and with the help of linguistic and non-linguistic factors, and audiences understand their intentions according to their own knowledge and concepts. This kind of PSAs presents the characteristics of structural adaptation and contextual adaptation, which play an important role in the advertising effect.

Vague Language
Vague language, which includes vague items (general nouns, general verbs, general extenders, vague clauses, clause-final ellipsis, and conversational implicature) and vague modifiers (vague quantifiers and other epistemic stance markers), is a feature of many languages, signaling a friendly attitude and modifying face threats (Cutting, 2015). For instance, Yan (2009) conducted a qualitative and quantitative analysis through a self-built corpus and categorized vague language in PSAs in terms of phonology, lexis, syntax, and pragmatics. Taking the Hefei city construction PSAs as an example, Huang (2011), designed a specific corpus and conducted a comprehensive study on the embodiment, causes, and effects of vague language in PSAs from the lexical and syntactic levels, as well as the cooperative principles, politeness theory and adaptation theory. It also analyses the importance of vague language in PSAs from the perspective of both the issuers and the audience. From the perspective of vague language, previous studies focused on the theoretical model of vague language, proving that it is a very important part of linguistics, and it is more convincing to combine it with the studies of PSA.

Pragmatic Debate
Dutch scholars Frans H. Van Eemeren and Rob Grootendorst proposed the idea of a critical discussion of persuading-oriented discourse from the perspective of pragmatics, gradually establishing pragmatic debate and promoting its development. The theory focuses on the ultimate goal of discourse argumentation, that is, to persuade the audience to accept its point of view to the greatest extent. For instance,  selected typical examples from a library of outstanding national radio and television PSAs and provided a comprehensive detailed case study. This study explained the strategies used in the four stages of discursive argumentation embodied in the antiepidemic PSAs.

Pragmatic Translation
Pragmatic translation theory is a new model in the translatory field, that is, applying the relevant research results of pragmatics to translation practices and translating on the basis of pragmatic and social pragmatic contrasts, so as to achieve equivalence in translation. Hu & Zhou (2009) used empirical analysis and analogy to explore the characteristics and methods of Chinese to English translation of PSAs from the perspective of linguistic equivalence. The study indicated that the comprehensive consideration of linguistic equivalence and social equivalence play an important role in the Chinese to English equivalence translation of PSAs, and the acceptability of different cultural readers becomes key to measuring the translation effectiveness.

Presupposition
There are a number of different approaches to presupposition, or what we might call presupposition phenomena in critical discourse analysis and adjacent disciplines. According to Alexandra (2014: 1), "this heterogeneity can at best lead to methodological confusion among students and scholars new to critical discourse analysis, while at worst it can lead to accusations of opaque or even unsound analysis". Under the idealized cognitive model, Zhu (2016) explored the phenomenon of linguistic presupposition in Chinese PSAs with the help of a self-built corpus. It clarified the relationship between the idealized cognitive model and the phenomenon of pragmatic presupposition and cognitively explained three types of pragmatic presupposition: propositional, metaphorical, and metonymic, in order to enrich the PSA system from the perspectives of both ad designers and audiences.

Intertextuality
In his Dictionary of Narratology, Gerald Prince, a famous narratologist, gives a relatively clear and understandable definition of intertextuality: the relationship between a certain text and its citation, adaptation, absorption, expansion, or overall transformation, which can be interpreted in this text (Cheng, 1996). Interdiscursivity belongs to a kind of intertextuality. Wang & Ding (2020) systematically analyzed PSAs with both social significance and profit-making roles, showing that interdiscursivity plays an important role in the understanding of discourse categories and contexts and that PSAs have positive significance in terms of corporate operations and social responsibility.

Pragmatic Failure
With the help of a self-built corpus, Cheng (2009) analyzed the rhetorical, strategic, and stylistic errors in PSAs from a pragmatic failure perspective. This study explored the causes and solutions and showed that solving the pragmatic failure is crucial to improving the effectiveness and persuasiveness of PSAs.
To summarize, all of the above-mentioned investigations have conducted in-depth analyses from specific perspectives in pragmatics, while some scholars have also established a complete pragmatics system and conducted a comprehensive analysis of PSA phrases from a macro perspective. For example, using a self-built corpus, Li (2017) summarised and analyzed the linguistic phenomena existing in PSA language from a pragmatic perspective, and further illustrated the positive impact of PSAs' pragmatic functions from different perspectives on their persuasive effects, as well as the strategy of expressing PSAs through conforming to the audience's psychological world. Xiong & Zhang (2017) selected a small number of samples for descriptive analysis to classify and interpret the language of instructions in PSAs from a pragmatic perspective with the help of specific examples. This study revealed that PSA language is divided into three categories: person, time, and space, and further indicated its function, connotation, and pragmatic effect from the audience's perspective. Yang (2013) systematically elaborated PSA language from multiple perspectives, including pragmatics, rhetoric, cognitive linguistics, and modern Chinese, through literature research, statistical and comparative analysis, and compared the language strategies in it from both positive and negative aspects.  used case studies to explain four English PSAs from four pragmatic principles: cooperation, politeness, power, and praise, with a view to providing a reference for the creation of PSAs in China. Yang (2012) also introduced the embodiment and functions of the cooperative principle and indirect speech act theory in pragmatics in the advertising language and investigated the application of this theory in the campus public welfare advertising language from a dialectical perspective.
In addition, apart from linguistic investigations of domestic PSAs, some scholars have also turned their perspectives to the comparison of the PSA language between China and other countries. For example, Cao (2018) compared the language of PSAs in China and South Korea in four aspects: syntax, vocabulary, rhetoric, and pragmatics and analyzed the linguistic similarities and differences between PSAs in China and South Korea. The analysis of the linguistic similarities and differences between the PSAs of China and Korea and the reasons for them were also presented in order to inspire the creation of PSAs.

Cognitive Linguistics
From the perspective of cognitive linguistics, PSA language usually starts from metaphor or metonymy and exemplifies through relevant models. Li (2018) conducted a qualitative analysis of the cognitive mechanism, metaphor types, characteristics, and functions of PSAs from the perspective of cognitive theory based on Lakoff's conceptual metaphor theory. The study found some problems in PSAs and proposed corresponding improvement measures. Using a self-constructed corpus, Xiao (2016) categorized the conceptual metaphor theory from a cognitive linguistic perspective, and explained the characteristics, functions, and significance of its embodiment in PSAs, revealing the important role of cognitive linguistics in the expression and public acceptance of PSAs. Chen & Tang (2020) used case study methods to analyze the relationship between text modality and image modality in PSAs. The combination of text modality and image modality in PSAs was analyzed through the conceptual metaphor and metonymy theory, and the relationship between the text and the relationship within different images was categorized and analyzed through cognitive mechanisms to show its embodiment and role in PSAs. Zhou (2016) analyzed a PSA on anti-corruption and incorruptibility as an example through a cognitive linguistic perspective in the form of a case study. The use of textual, visual, and auditory multimodal means in different stages under the conceptual metaphor theory is of great significance to the persuasive effect of PSAs. Dong & Shi's (2019) cognitive linguistic study of multimodal metaphors in PSAs was basically the same as Zhou Xian's approach and perspective, while the theoretical analysis is more comprehensive. From the perspective of metaphor or metonymy, these studies have found that cognitive linguistics can not only improve the ideological and artistic level of the whole PSAs, so as to produce good social effects, but also enable the audience to have a new understanding and cognition of the metaphor.

Multimodal Perspective
The research of multimodal perspective is mainly carried out from the combination of theoretical means such as graph, text, and semiotics. Li (2006) used content analysis and a self-constructed corpus for statistical and descriptive analysis to elaborate on Chinese print PSAs in terms of both textual and pictorial modality from both linguistic and semiotic perspectives. This paper also compared PSAs with commercial advertisements to reveal the distribution characteristics of lexical, syntactic, and diction aspects, as well as visual symbolic features in Chinese print PSAs from a linguistic perspective. By combining qualitative and quantitative approaches and using a selfconstructed corpus, Zhou (2014) conducted a comparative and comprehensive analysis of the language of Russian PSAs from multimodal perspectives, including linguistic and pictorial modalities, and confirmed the interdependence between linguistic and non-linguistic modalities in Russian PSAs and the positive impact of their application on the function of PSAs. Li (2018) combined provided a study by means of a self-constructed corpus, taking the combined graphic and textual print PSA language as the main research object, selecting the works of Xiangtan City advertising corpus, classifying such PSAs, and systematically elaborating the relationship between graphic and textual language, the characteristics and functions of the advertising language. These studies have found that Chinese PSA is unique in both language and image modes, which provides a meaningful topic for the study of PSA language.

Rhetoric
Rhetoric is defined as a function that identifies possible ways of persuasion on any given issue (He, 2001). The papers collected in this study focused on the linguistic features of PSA language from two perspectives of rhetoric and variational rhetoric. With the help of an analysis of a self-built corpus, Xia (2007) systematically analyzed the PSA language from a sociolinguistic perspective in terms of discourse, rhetoric, and the principles of cooperation and politeness in discourse found the mistakes in PSA language and their causes and elaborated on the factors influencing the effectiveness of PSAs from the audience's perspective. Similarly, Wu (2018) used a new perspective of variational rhetoric to illustrate the phonological, lexical, and grammatical variation of PSAs in the new era, and analyzed the positive effects of variational rhetoric on the effectiveness of PSAs with examples, in order to provide new ideas for the creation of PSAs. Feng (2012) uses a top-down analysis model to analyze the rhetorical features and principles of PSA language from the sociolinguistic and "humanistic" perspectives of pragmatics, illustrating the principles of cooperation and politeness in PSA language and their important influence on the acceptability and persuasiveness of PSAs. To summarize, in order to better spread its theme and achieve its purpose of persuasion and education, the designers of PSAs often use some rhetorical means to make their language more precise and forceful.

Systemic-functional Linguistics
Systemic-functional linguistics mainly starts from Halliday's Systemic-functional grammar, which offers a basic model of analyzing interpersonal meaning to researchers by investigating interpersonal meaning from mood, modality, and person system in dialogues (Halliday, 1994). For instance, Du (2014) used a combination of qualitative and quantitative approaches to systematically analyze the phrases of multinational English environmental PSAs from a humanistic perspective using a self-built corpus and explored the embodiment and efficacy of the four systems of tone, mood, person, and evaluation in such PSAs from a systemic functional linguistic perspective, with a view to helping the advertise issuers and audiences jointly establish a good PSA mechanism. Zhu (2018) and Du (2014) adopted essentially the same research approach, exploring the interpersonal meaning of English-Chinese environmental PSAs from the perspective of systemic functional linguistics, and verifying the feasibility of systemic functional linguistics in the comparison of English and Chinese PSAs through the comparison of the similarities and differences in the systems of tone, mood, and person between the two languages while proposing a new perspective on the improvement of the PSA system.

Ecolinguistics
Ecolinguistics is a relatively new research perspective, relatively little research has been conducted on the language of PSAs from an ecological linguistic perspective, and only one piece of study has been collected, namely an example analysis of environmental news and PSAs by , which revealed the important role of such texts in promoting ecological construction.

Conclusion
This study provides a review of the papers on PSAs from the perspective of linguistics in the past fifteen years (2006-2021) and finds that most of the relevant studies focus on pragmatics, such as the speech act theory, politeness theory, cooperation principle, association-adaptation theory and other representative models reflecting the interpersonal meaning of PSAs. At the same time, the analysis of the words and phrases of PSAs has also been conducted from different perspectives, such as rhetoric, conceptual metaphor theory, and Systemic-functional linguistics, and has made a more indepth and comprehensive linguistic study. In addition, some scholars have been able to use some statistical methods and field surveys to select areas where research is relatively weak, such as discursive presupposition, graphic modality, and environmental texts, to conduct in-depth studies, providing a new direction for linguistic research on PSAs.
But at the same time, through the literature review, it can be seen that the number of studies from a linguistic perspective of PSAs is still limited. In addition, the corpus used in the previous studies is mostly self-built and lacks authority and objectivity from sources. Besides, the sample size is relatively small and the research scope is narrow. Furthermore, there are great differences between languages and cultures in different countries, but there are relatively few comparative studies on the terms used in public service advertisements in different languages. Finally, due to the difficulty in systematically obtaining corpus data of public service advertisements, most linguistic studies on PSA remain on the level of qualitative analysis, leaving a gap in quantitative empirical studies.
Based on the above shortcomings, future studies can be conducted by selecting a large number of samples from the official corpus for quantitative statistical analysis and making visual charts, or by collecting first-hand data through field surveys. At the same time, it is important to collect data on different languages and cultures for comparative analysis, in order to comply with the trend of conducting cross-disciplinary and cross-cultural studies. It is also important to determine the appropriate target audience and scope of research, and the use of 'humanistic thinking' from the audience's point of view is essential for PSAs to make a real difference.
In short, successful PSAs have a positive effect on the behavior of their audiences, and their language has a significant impact on the function and effectiveness of advertising. The study of PSA language from the perspective of linguistics, which has undergone a long history of development, has taken on a new dimension in the new era and is of great significance in expanding the field of academic research and promoting innovation and acceptance of PSAs. Of course, there is still much room for exploration of related research.