pledging vs tie that binds

pledging

noun
  • The making of a pledge. 

tie that binds

noun
  • Something shared between two or more people, such as an interest, hobby, or experience, that causes their relationship with each other to strengthen. 

  • Used other than figuratively or idiomatically: tie#Noun. 

How often have the words pledging and tie that binds occurred in a corpus of books? (source: Google Ngram Viewer )