causal vs preparatory

causal

adj
  • of, relating to, or being a cause of something; causing 

noun
  • a word (such as because) that expresses a reason or a cause 

preparatory

adj
  • Of or pertaining to preparation, having the purpose of making something or someone ready, preparative. 

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