constrain vs liberate

constrain

verb
  • To force physically, by strong persuasion or pressuring; to compel; to oblige. 

  • To keep within close bounds; to confine. 

  • To reduce a result in response to limited resources. 

liberate

verb
  • To release from restraint or inhibition. 

  • To release from chemical bonds or solutions. 

  • To acquire from an enemy during wartime, used especially of cities, regions, and other population centers. 

  • To release from servitude or unjust rule. 

  • To release from slavery: to manumit. 

  • To acquire from another by theft or force: to steal, to rob. 

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