http://info.borland.com/techpubs/delphi/delphi5/opl g/classes.html

You can increase the visibility of a member in a descendant class by redeclaring it, but you cannot decrease its visibility. For example, a protected property can be made public in a descendant, but not private. Moreover, published members cannot become public in a descendant class. For more information, see "Property overrides and redeclarations".