permissive vs unprescriptive

permissive

adj
  • Giving permission, or predisposed to give it; lenient. 

  • That allows the replication of viruses. 

  • Open to the public by permission of the landowner. 

unprescriptive

adj
  • not prescriptive 

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