imperfect tense vs imperfective

imperfect tense

noun

  • A tense used to describe a past action that is ongoing, incomplete or continuous, or coincident with another action. 

imperfective

noun

  • The imperfective aspect; a verb having this aspect. 

adj

  • Of, relating to or having the properties of the imperfective aspect. 

How often have the words imperfect tense and imperfective occurred in a corpus of books? (source: Google Ngram Viewer )