現代漢語中一般將介詞"對"和"向"看作近義詞，然而對其硏究多互釋，少辨析，且矛盾之處甚多。本文通過對介詞"對"和"向"語法化過程的梳理，發現兩者分別以"引進對象"和"引進方向"兩義項爲主線平行發展，只不過在發展過程中出現過交集。基于此，本文認爲現代漢語中兩者不存在共同義項，只是當句中介詞賓語和謂詞同時含有[+方向性]和[+對象性]兩大義素時，存在最大的替換可能性。

In the modern Chinese, the prepositions "對"and ``向" are considered as a pair of synonyms to introduce an object. However, the research on them focuses more on explanation and less on discrimination with many contradictions. In view of this, this thesis does a research from the perspective of grammaticalization and finds that the prepositions "對" and "向"develop in parallel with "introduction of an object" and "introduction of a direction" as mainlines respectively. They have intersections in the process of development. On the basis of this, the author holds that they don`t have common meanings but are most likely to be replaced by each other only when the prepositional phrases and predicates both contain [+ directional] and [+ object] in the sentences.