incommutable vs perpetual

incommutable

adj
  • Not commutable 

perpetual

adj
  • Continuing; uninterrupted. 

  • Set up to be in effect or have tenure for an unlimited duration. 

  • Lasting forever, or for an indefinitely long time. 

  • Flowering throughout the growing season. 

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