motivate vs weaken

motivate

verb
  • To animate; to propel; to cause to take action 

  • To provide someone with an incentive to do something; to encourage. 

weaken

verb
  • To make weaker or less strong. 

  • To become weaker or less strong. 

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