In ordinary language, to call a copyright a "property" right is a bit misleading, for the property of copyright is an odd kind of property. . . . I understand what I am taking when I take the picnic table you put in your backyard. I am taking a thing, the picnic table, and after I take it, you don't have it. But what am I taking when I take the good idea you had to put a picnic table in the backyard—by, for example, going to Sears, buying a table, and putting it in my backyard? What is the thing that I am taking then?
The point is not just about the thingness of picnic tables versus ideas, though that is an important difference. The point instead is that in the ordinary case—indeed, in practically every case except for a narrow range of exceptions—ideas released to the world are free. I don't take anything from you when I copy the way you dress—though I might seem weird if I do it every day. . . . Instead, as Thomas Jefferson said (and this is especially true when I copy the way someone dresses), "He who receives an idea from me, receives instruction himself without lessening mine; as he who lights his taper at mine, receives light without darkening me."