As I see it, a major component  of our commerc
> ial system is the various ways people and entities are liable on
> commercial paper.   Without those established liabilities, the credit
> and payment system simply will not work.
>
I'd add (I am chatty today) that it is crucial to understand what is
NOT a negotiable instrument -- i.e. the credit card slips that
merchants accept for goods and services, and a host of other pieces of
paper that are, in some sense, money substitutes but are not
negotiable instruments.
 
I often start out explaining it this way: Money travels (probably to
Chicago, but maybe Omaha or Akron) without baggage; negotiable
instruments have carry-on luggage; other money substitutes check
varying amounts of baggage.
 
G