a priori vs imperative

a priori

adj
  • Presumed without analysis. 

  • Self-evident, intuitively obvious. 

  • Based on hypothesis and theory rather than experiment or empirical evidence. 

  • Developed entirely from scratch, without deriving it from existing languages. 

adv
  • In a way based on theoretical deduction rather than empirical observation. 

imperative

adj
  • Having semantics that incorporates mutable variables. 

  • Expressing a command; authoritatively or absolutely directive. 

  • Essential; crucial; extremely important. 

  • Of, or relating to the imperative mood. 

noun
  • A verb in imperative mood. 

  • The grammatical mood expressing an order (see jussive). In English, the imperative form of a verb is the same as that of the bare infinitive. 

  • An essential action, a must: something which is imperative. 

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