2. Syntactic Relations (句法关系) (1) Positional Relation (位置关系) Positional relation, refers to the sequential arrangement of words in a language. It is the basic syntactic relation, and also the requirement of grammatical acceptability and semantic intelligibility of human language. (2) Relation of Substitutability (替代关系) The relationship of substitutability refers to classes or sets of words grammatically substitutable for each other in sentences with the same structure, or groups of more than one word which may be jointly substitutable grammatically for a single word of a particular set. (3) Relation of Co-occurrence (同现关系)