Some handy concepts

• Externalities
  An externality is a cost* of an action that falls upon people other than the one(s) taking the action. If Laura buys gas for her car and goes for a drive, the exhaust (and its effect on those downwind, or on those down dimension #4) is an externality. Likewise, if Bob's dog barks whenever he's gone, the noise is an externality borne by Bob's neighbors.
  


• Emergent properties
  Emergent properties are properties that emerge due to even simple interactions within a system.
  For example, given the following conditions:
  • a bad thing is happening
    
  • public opinion could curtail the bad thing
    
  • public opinion is influenced by newspaper articles
    
  • newspaper articles give equal voice/weight/credibility to both sides of an issue, if they can find someone to present that side.
    
  • Someone with wealth has a vested interest in the bad thing not being curtailed
    
  • people/groups exist who are willing to say that the bad thing is not happening (or not bad, or not curtailable), in exchange for some wealth
    
  THEN (here comes the emergent property)
  Even if there is no substantive disagreement among credible experts that the bad thing is happening, public opinion will still be that there is wide disagreement among credible experts as to whether it is happening.
  
  Another emergent property: for the vast majority of topics, the information in Wikipedia articles is accurate.* Exercise for the reader: how could this property emerge from a system in which almost anyone can edit almost any article?
  
  And another: overall, people who accord public relations the same credibility as science will emerge less well informed than those who don't.