Copyleft licensing is permissive licensing with additional conditions. Larry Rosen made this point with his Academic Free License and Open Software License. T

Copyleft licensing is permissive licensing with additional conditions. Larry Rosen made this point with his Academic Free License and Open Software License. They're the same form, with just one difference, in 1(c). That difference turns the AFL, a permissive license, into the OSL, a copyleft license. Copyleft license conditions beg interpretive questions about what actions trigger copyleft requirements and what actions satisfy those requirements. Common copyleft licenses differ in their triggers and requirements, as well as how they express them in the legal text.