Constituents that can be substituted for one another without loss of grammaticality belong to the same syntactic category.
可以相互替换而又不改变语法属性的成分属于同一句法类型。
英语百科
Syntactic category
A syntactic category is a type of syntactic unit that theories of syntax assume. Word classes, largely corresponding to traditional parts of speech (e.g. noun, verb, preposition, etc.), are syntactic categories. In phrase structure grammars, the phrasal categories (e.g. noun phrase, verb phrase, prepositional phrase, etc.) are also syntactic categories. Dependency grammars, however, do not acknowledge phrasal categories (at least not in the traditional sense).