“同语”作为一种修辞现象被陈望道先生归入复叠和警策两种修辞格之中（《修辞学发凡》）。将这种现象正式命名为“同语”的是张弓先生（《现代汉语修辞学》）。因此，文章立足于修辞学，尝试进行语法与修辞的互动研究，运用语法学、修辞学中的相关理论，对同语现象进行探讨，从而将同语区分为修辞同语和语法同语。修辞同语的主语和宾语虽然同形，但主语表示指称意义，宾语表示属性意义，宾语的含义比主语“更复杂”。语法同语的主语和宾语同形，而且意义相同。文章分别从句法、语义和修辞三个方面对语法同语和修辞同语进行详细讨论。 在句法结构方面，修辞同语的主语表示指称意义，宾语表示属性意义，搭配使用的谓语是表示恒常属性的属性谓语，因此，将其结构模型描写为[指称性XP+属性谓语+述谓性XP]。语法同语的主宾语和谓语都没有太多的限制，主宾语既可以都表示指称意义，也可以都表示述谓意义；谓语既可以是属性谓语，也可以是事件谓语；因此，将其结构模型描写为[指称性XP+事件/属性谓语+指称性XP]或[述谓性XP+事件/属性谓语+述谓性XP]。同语从结构上又可以分为基本式和变式，前后项XP完全相同的形式即为基本式，变式包括前项XP有修饰语的单项式以及多项同语式，其中，多项同语式又可分为对举式和并列式。 在语义特征方面，修辞同语可以解读为“XP具有XP的特征”；语法同语具有多种解读模式，可以表示“让步”“强调事实”“区分清楚”等语义，还可以通过固定结构表达固定意义。 在修辞特点方面，着重从对语境的依赖和篇章分布特点两个方面进行探讨。语境可能会影响对语法同语和修辞同语的判断，修辞同语的语境一般会对其所强调的属性特征进行详细描述，语法同语的语境则不会有相关的描述。语境也可能会影响修辞同语的解读，相同的同语结构在不同的语言环境下可能会强调不同的属性特征，具体的语义解读可能会不同。在篇章分布方面，修辞同语可以与上下文构成转折、因果、并列、递进等关系；语法同语可以与前后文构成转折、因果、假设等关系；二者都主要用于转折关系，但是修辞同语主要用于转折复句的正句，而语法同语则主要用于让步转折复句的偏句。此外，二者的区别还体现在语法同语可以充当句法成分，而修辞同语几乎没有这种用法。

Tautology is a kind of rhetorical phenomenon, Chen Wangdao noted that first in 1932. It was named by Zhang gong first in 1963, and Zhang gong pointed out that if the subject and object are expressed in the same word, and the sentence made up of them indicates judgment, the sentence is called tautology. The subject and object are expressed in the same word, but the meaning are not the same. The meaning of the object is more complicates than that of the subject. Based on rhetoric, the paper tries to do the research on the interaction between grammar and rhetoric, and discusses tautology by using the theories of grammar and rhetoric. Accordingly, it distinguishes tautology in rhetoric from tautology in grammar. In tautology in rhetoric, the subject and object are expressed in the same word, but the meaning of the object is more complicates than that of the subject. In tautology in grammar, the subject and object are expressed in the same word, and their meaning are also the same. Afterwards, the paper discusses tautology in rhetoric and tautology in grammar in detail from three aspects: structural features, semantic features and rhetorical features. In terms of the structural features of tautology, In tautology in rhetoric, the subject is referential, the object is predicative, and the predicate is individual-level predicate, as a result of this, the model of structure of tautology in rhetoric can be described as [referentiality XP+individual-level predicate+predication XP]. In tautology in grammar, there are not too many restrictions on the subject, the object and the predicate, so the model of structrre of tautology in grammar can be described as [referentiality XP+stage-level predicate/ individual-level predicate+ referentiality XP]. The structural form of tautology can be divided into basic form and variant form. Basic form is the form that the former XP is exactly the same as the later XP. Variant form includes the former XP has modifier and multinomial, and the multinomial can be divided into parallel dtructure and coordinate structure. In terms of the semantic features of tautology. Tautology in rhetoric can be interpreted as “XP has the characteristics of XP”. Tautology in grammar has many different interpretations, it can indicate concession, emphasize facts, emphasize distinction, and express fixed meanings through fixed structures. In terms of the rhetorical features of tautology, mainly analyzes context dependence and the features of discourse. Context may affect the judgment of tautology in rhetoric and tautology in grammar. The context of tautology in rhetoric generally describes in detail about the predicative characteristics that it emphasizes, but the context of tautology in grammar do not have relevant descriptions. Context may also affect interpretation of tautology in rhetoric. Because different context may emphasize different predicative characteristics, the same form of tautology may have different interpretation. In discourse, tautology in rhetoric can be related to the preceding and the following text. Tautology in grammar can be related to the preceding and the following text, and can act as syntactic elements. There are some commonness and difference between them. Both tautology in rhetoric and tautology in grammar are mainly used in transitional complex sentences, but tautology in rhetoric mainly used as main clauses, and tautology in grammar mainly used as modifier clauses. In addition, tautology in grammar can act as syntactic elements, but tautology in rhetoric have no such usage.