build castles in the air vs purpose

build castles in the air

verb
  • To have any desire, idea, or plan that is unlikely to be realized; to imagine visionary projects or schemes; to have an idle fancy or a pipe dream; to daydream. 

purpose

verb
  • To have or set as one's purpose or aim; resolve to accomplish; intend; plan. 

  • To have (an) intention, purpose, or design; to intend; to mean. 

noun
  • meaning for existing or doing something. 

  • Resolution; determination. 

  • Function, role. 

  • The end for which something is done, is made or exists. 

How often have the words build castles in the air and purpose occurred in a corpus of books? (source: Google Ngram Viewer )