An intellectual work that is eligible for copyright passes into the public domain when that copyright expires, is released, or is not properly perfected. An intellectual work in the public domain may be freely copied by anyone.
Some intellectual works pass into the public domain upon creation, such as court decisions. However, all copyrights eventually pass into the public domain, although that presently takes a long period of time on average. However, most works from the 19th century are all in the public domain.