1. The Source of Semantic Wave Theory

Bernstein proposed the knowledge structure theory in1999 with the consideration that different types of knowledge are presented by different types of discourses. He classified discourses into two types: vertical discourse and horizontal discourse. Generally speaking, horizontal discourse is the discourse used in people’s daily life. Meanwhile, vertical discourse refers to natural science discourse, social science discourse and humanities discourse. Aiming at distinguishing completely different knowledge structure of aforementioned discourses, he put up with the ideas of hierarchical knowledge structure.

Based on knowledge structure theory, Karl Maton put forward knower structure, and he believed that every knowledge structure corresponds to a knower structure. Afterwards, Maton proposed legitimation code theory, LCT for short, which comprises five elements: Density, Autonomy, Specialization, Temporality and Semantics. Subsequently Maton proposed the conception of Semantic Wave on the basis of semantics element. The formation of semantic wave mainly relies on two factors, namely semantic density and semantic gravity. Because the semantic wave is to investigate crucial features of knowledge accumulation, this view attract great attention of systemic functional linguists. However, the idea of semantic wave was brought up from social pedagogy aspect, which needs to be transformed for adapting theories of systemic functional linguistics. Then Martin put up ideas of mass and presence in accordance with semantic density and semantic gravity. He combined them with metafunctions of systemic functional linguistics, and studied the generation and interpretation of discourse meaning from three perspectives: ideational function, interpersonal function and textual function.

2. Basic Content of Semantic Wave Theory

As is mentioned before, the formation of semantic wave depends on semantic density and semantic gravity. Semantic gravity is the degree of semantic dependence on its discourse; semantic density refers to degree of semantic concentration of a certain discourse. In a discourse, semantic gravity is usually inversely proportional to semantic density. Sentences with high semantic gravity tend to have low semantic density, and those with low semantic gravity always have high semantic density. More specifically, spoken languages in our daily life are of high semantic gravity and low semantic density, but academic languages in colleges and universities are of low semantic gravity and high density. Especially when a term is introduced into a course, this new term tends to have high semantic density but low semantic gravity. At this time, teachers usually design a lead-in part to introduce background information about this term to reduce its semantic density. After presenting this new term to students, teachers should explain this term to students, which make the term easier understood by students via reducing its semantic density. Then teachers often generalize information about the term to reintroduce this term to students by increasing its semantic density. In summary, the process of knowledge practice is a process alternated with unpacking difficulties and repacking knowledge.

3. Application of Semantic Wave Theory

3.1 Application of Semantic Wave Theory in Teaching and Learning

Because semantic wave theory originated from knowledge accumulation practice, its application deeply rooted in school teaching and learning. Current applications of semantic wave theory center on designing of teaching process, teaching evaluations and compiling of textbooks.

In the field of designing of teaching process and teaching evaluations, semantic wave is a reasonable way to realized accumulative knowledge construction from the perspective of student knowledge acquisition. In classroom conversations, students can integrate new knowledge with original knowledge by following the semantic wave formed by the strong and weak changes of semantic gravity and semantic density in the teacher’s discourse, thereby realizing cumulative knowledge construction. Besides, it is believed that a teaching approach alternated with unpacking difficulties and repacking knowledge is a desirable teaching method. What’s more, the semantic wave can be utilized in evaluations of teaching effects. Whether a teacher’s teaching process followed by scientific rules of semantic wave can be another standard to gauge a teacher’s teaching skills.

3.2 Application of Semantic Wave Theory in Discourse Analysis

Except for what we have mentioned before, semantic wave theory can also be applied to discourse analysis. To assign a sentence with concrete semantic gravity and semantic density, we can illustrate the semantic wave of a paragraph, even a whole passage. Cloran (1994,1995,2010) conceptualizes the semantic of context dependence based on the central entity value in the message and event orientation, which is called the Rhetoric Unit. The rhetorical unit is a semantic unit between the context and the message at the structure level. In the view of Cloran and Hasan, the rhetorical unit is the expression of the language function of social processes, located between the two poles of the constitutive and auxiliary social activities, as shown in the following:

Action-Commentary-Reflection-Observation-Report-Recount-Plan-Prediction-Account-Conjecture-Generalisation

ancillary constitutive

It is suggested that these classes of RU are expressions of the role of language in the social process. Hasan (1985) conceptualises this contextual variable as a continuum at the left extreme of which language is ancillary to the task in hand and at the right extreme language constitutes the social activity. In the above-mentioned gradual change group, the central entity of the rhetorical unit near the auxiliary end is the interactant or other person object that is copresent in the material situation, and the referred event concurrent with the time of speaking, thus constituting the action rhetorical unit. The central entity of the rhetorical unit near the constituent end is the entity that does not exist at the speaking moment. The event orientation is also generalised: it does not refer to any specific time but rather is timeless or habitual, and thus this kind of rhetorical units constitutes the generalization rhetorical unit. Based on this proposal, it can be seen that the central entity value of the discourse unit itself and the event orientation it refers to indicate its typical context-dependent characteristics, ie. the auxiliary rhetorical unit is contextualized language use, while the constituent rhetorical unit is decontextualized language use (Cloran1994). This characteristic is consistent with the semantic gravity under the semantic principle of LCT, that is, it reflects the degree of dependence and independence of meaning on the context(Luo Zaibing，2019). From the perspective of the semantic gravity of LCT, the action rhetorical unit at the left end is the closest to the current discourse context (Cloran1994) because of its entity and reference, so it has the highest degree of context dependence. Luo Zaibing (2019) assigns its semantic gravity and semantic density to SG10, SD1. The generalisation rhetorical unit at the right end is non-immediate reference because its central entity is a fictitious event, which is the most out of context and has the lowest degree of context dependence. Therefore, it can be seen that its semantic attraction is the lowest and the semantic density is the highest. Luo Zaibing (2019) assigns its semantic gravity and semantic density to SG0, SD11, and the specific semantic gravityand semantic density values of each discourse unit are shown in the figure below:

Rhetorical unit	SG	SD	Rhetorical unit	SG	SD
Generalization	SG0	SD11	Report	SG6	SD5
Conjecture	SG1	SD10	Reflection	SG7	SD4
Prediction	SG2	SD9	Observation	SG8	SD3
Plan	SG3	SD8	Commentary	SG9	SD2
Account	SG4	SD7	Action	SG10	SD1
Recount	SG5	SD6

In any context, as a constitutive and auxiliary rhetorical unit, it can objectively and explicitly describe the specific scale of semantic gravity and semantic density, and objectively and concretely define the fluctuation and continuity of semantic waves. The aforementioned semantic wave assignment framework is based on the reciprocity of semantic gravity and semantic density. It highlights the specific movement process and the degree of semantic fluctuations of the semantic wave, and provides an objective and explicit measurement scale for the description of the specific fluctuations of the semantic wave.

Chosen by Cloran.C, the transcribe outcome of a discourse was shown in the paper Rhetorical unit analysis and Bakhtin’s chronotype. First the discourse was transformed from PDF to TXT. As is shown in the picture, there are30 rhetorical units in the selected discourse. Then the discourse was imported into UAM Corpus Tool version3.3 to build a self-made corpus.

Based on theoretical framework proposed by Cloran.C and Luo Zaibing, we can use the function of manual annotation in UAM Corpus Tool version3.3 to address the selected discourse.

According to Luo Zaibing’s assignment of rhetorical units, we can make a diagram of semantic wave of selected discourse with the help of Matlab2021.

As the figure7 showing to us, the movement direction of the semantic wave can be divided into ascending, descending, parallel, ie. there are semantic fluctuations. The rising direction of the semantic wave means that the semantic gravity is weakened and the semantic density is strengthened. The presented knowledge reflects the tendency of contextualization. The knowledge structure shifts to the higher-level knowledge structure, just as the action rhetorical unit of “SG10, SD1” move to generalization rhetorical unit of “SG0, SD11”. The decline of the semantic wave means that the semantic gravity is strengthened, and the semantic density is weakened. The presented knowledge reflects the tendency of context dependence. The structure of knowledge moves to the structure of common sense knowledge, just as the recount rhetorical unit of “SG5, SD6” move to commentary rhetorical unit “SG2.SD9”.

Previous studies have shown that the high semantic level of the semantic wave is not conducive to the knowledge structure crossing the semantic gap of the specific context, while the semantic wave of the low semantic level is not conducive to the structuring of knowledge in the specific context, and the fluctuating semantic wave is the key to bridging the knowledge gap (Maton2013).

However, the aforementioned assignment scale is a tentative study conducted by Chinese scholar. There still lacks an authoritative assignment scale for semantic wave theory, we still need more time to conduct numerous researches on semantic wave theory.

参考文献：

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