immutability vs perpetuity

immutability

noun
  • The state or quality of being immutable; immutableness. 

  • The state of being unchangeable in the memory after creation. 

perpetuity

noun
  • The quality or state of being perpetual; endless duration; uninterrupted existence. 

  • An annuity in which the periodic payments begin on a fixed date and continue indefinitely. 

  • Something that is perpetual. 

  • A limitation intended to be unalterable and of indefinite duration; a disposition of property which attempts to make it inalienable beyond certain limits fixed or conceived as being fixed by the general law. 

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