the problem is if you ask a Russian what the other word (in the pair perfective/imperfective) they won't know As a foreigner learning the language we are taught to learn them in pairs, but that wont' work for you on the street of Novgorod. And after you explain, or give examples, they won't be able to give you an exactpair because as soon as one starts adding prefixes it becomes perfective (but not necessarily the dictionary pair) not to mention other ways it gets complicated