alteration vs clarification

alteration

noun
  • The act of altering or making different. 

  • The state of being altered; a change made in the form or nature of a thing; a changed condition. 

clarification

noun
  • The act of freeing from obscurities. 

  • The act of clarifying; the act or process of making clear or transparent by freeing visible impurities; particularly, the clearing or fining of liquid substances from feculent matter by the separation of the insoluble particles which prevent the liquid from being transparent. 

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