「知道」和「認為」是表達認知模態的基本命題態度謂詞。「知道」在辭彙語義結構中不僅包含（1）『認知狀態主體在其意識中有命題P』，而且包含（2）『P的所指在現實世界裏是有的』成分，在語用方面主要充當句子交際結構的述位元。「認為」只表示成分（1），不含成分（2），在句子的交際結構中大多充當主位元的成分。兩個謂詞的句子交際結構位置、所支配命題的表達手段和替代方式、疑問標記、與否定詞的意義關係、修飾語類型以及能否構成主位對比疑問句等方面，有一系列對立的表現，這些句法差異都可以從它們的辭彙語義、語用特徵中求得解釋。

ZHIDAO and RENWEI are both basic predicates of propositional attitude,
expressing the epistemic modality. In the semantic structure, ZHIDAO expresses not only a) that the epistemic subject has the proposition P in his mind, but also b) what P refers to exists in the reality. ZHIDAO acts as the rhyme in the communicative structure pragmatically. RENWEI, on the other hand, expresses only a), but not b). RENWEI usually acts as the theme in the communicative structure. These two predicates demonstrate contrasting behaviors in word order of the communicative structure, in the
expressing means and referential method of subordinate proposition, in the interrogative marker, in the object of negation, in the types of modifiers, as well as in the possibility of forming the theme-only interrogation. The interpretation of these different syntactic
behaviors of the two predicates can be obtained through the analysis of their lexico-semantic and pragmatic characteristics.