observant vs unthinking

observant

adj
  • Diligently attentive in observing a law, custom, duty or principle; regardful; mindful. 

  • Alert and paying close attention; watchful. 

unthinking

adj
  • Showing no regard; careless or unconcerned. 

  • Without proper thought; thoughtless. 

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