inconsistent vs unstable

inconsistent

adj
  • Not compatible (with another thing); incompatible, discrepant, at odds. 

  • Lacking internal consistency; self-contradicting; not compatible with itself. 

  • Not consistent or coherent in thought or behavior. 

  • Having the property that a contradiction can be derived. 

unstable

adj
  • Unpredictable. 

  • Readily decomposable. 

  • Not stable. 

  • Radioactive, especially with a short half-life. 

  • Fickle. 

  • Having a strong tendency to change. 

  • Fluctuating; not constant. 

verb
  • To release (an animal) from a stable. 

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