constancy vs inconstancy

constancy

noun
  • The quality of being constant; steadiness or faithfulness in action, affections, purpose, etc. 

  • An unchanging quality or characteristic of a person or thing. 

inconstancy

noun
  • Lack of constancy; lack of consistency in thought, emotion or action. 

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