build castles in the air vs conceive

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. 

conceive

verb
  • To develop an idea; to form in the mind; to plan; to devise; to originate. 

  • To understand (someone). 

  • To generate or engender; to bring into being. 

  • To become pregnant (with). 

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