inward vs on the surface

inward

adj
  • Not superficially obvious, inner, not expressed, especially relating to mental or spiritual faculties as opposed to external ones. 

  • Moving or tending toward the inside. 

  • Situated on the inside; that is within, inner; belonging to the inside. 

adv
  • Towards the inside. 

  • Towards one’s mind, thoughts, or internal self. 

on the surface

prep
  • apparently, outwardly; superficially 

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