你可以把它们看作介词，后置介词这个说法是有的，不过仅限于ago，aside，notwithstanding几个介词，传统上大家一般认为他们是副词。给你摘录点原文解释：A preposition comes before its complement; a postposition comes after its complement. English generally has prepositions rather than postpositions – words such as in, under and of precede their objects, such as in England, under the table, of Jane – although there are a few exceptions including "ago" and "notwithstanding", as in "three days ago" and "financial limitations notwithstanding". Some languages that use a different word order have postpositions instead, or have both types. The phrase formed by a preposition or postposition together with its complement is called a prepositional phrase (or postpositional phrase, adpositional phrase, etc.) – such phrases usually play an adverbial role in a sentence.----这种所谓的后置介词在《A Modern course in English Syntax 》49 也有简述：The normal order of elements in the PP is: P-NP（介词-名词短语）. However, English also has a number of postpositions, which typically follow their Complements（这个补语就是我们传统的介词宾语）, as in: three weeks ago and all joking aside; ago and aside are like prepositions in that they serve as the Head of a PP（介词短语）.