existence vs illusion

existence

noun
  • The state of being, existing, or occurring; beinghood. 

  • Empirical reality; the substance of the physical universe. (Dictionary of Philosophy; 1968) 

illusion

noun
  • The state of being deceived or misled. 

  • A misapprehension; a belief in something that is in fact not true. 

  • Anything that seems to be something that it is not. 

  • A magician’s trick. 

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