persuade vs soft-soap

persuade

verb
  • To successfully convince (someone) to agree to, accept, or do something, usually through reasoning and verbal influence. 

soft-soap

verb
  • To attempt to persuade by flattery or pleasing words; to butter up. 

noun
  • Persuasion by means of flattery or pleasing words. 

How often have the words persuade and soft-soap occurred in a corpus of books? (source: Google Ngram Viewer )