What is the difference between a copyright holder's right to use a copyrighted work without permission?

Similarity of expression must be established because it is an axiom of copyright law that copyright protects only an author's expression of an idea and not the idea itself. 17 U.S.C. Sec. 102(b); Mazer v. Stein, 347 U.S. 201, 217-218, 74 S.Ct. 460, 470-471, 98 L.Ed. 630 (1954). ¹ Corollary to this axiom is a strong policy permitting all to use freely the ideas contained in a copyrighted work so long as copyrighted expression is not appropriated.