incapable vs ineffectual

incapable

adj
  • Not capable (of doing something); unable. 

  • Not in a state to receive; not receptive; not susceptible; not able to admit. 

ineffectual

adj
  • Worthless; ineffective. 

  • Unable or insufficient to produce effect. 

  • Weak, indecisive; lacking forcefulness. 

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