Arbitrary conception? What does the Buddha mean by arbitrary conception in the Diamond Sutra?


  Then the lord Buddha made his meaning even more emphatic by saying:
  "Subhuti, when people begin their practice of seeking to attaining
  total Enlightenment, they ought to see, to perceive, to know, to
  understand, and to realize that all things and all spiritual truths
  are no-things, and, therefore, they ought not to conceive within their
  minds any arbitrary conceptions whatsoever."
All things we see are labeled by us human beings but are not the label,  they are just what they are. So when practicing mindfulness(involving seeing, perceiving, knowing and understanding for the purpose of transcending suffering), one experiences things directly as they are with no assumptions, labels, stories or judgements. In other words no "arbitrary conceptions".

If there is verbal thinking happening in one's mind, it is experienced as just a formation and the meaning of the words are conceptual so one doesn't need  to process the content, meaning or "story" of the thinking  even though we are so used to a kind of instant understanding of the conceptual meaning. 

If there is pain or pleasure it is a kind of assumption,  judgment or arbitrary conception when we react to it with aversion or clinging. When we are not seeing like this we are in a way just sleeping through life on autopilot in an impulse and arbitrary way.

Even if one could see like this at all times it doesn't mean they must stop understanding all concepts all the time of course.