For how many years is a copyright?
A copyright, unlike a patent, lasts for the entire life of the author, and international law is pretty much all the same in extending copyright protections for between 50 and 100 years after the author has died.
This gives the author legal protection for their published works, and sole ownership of them, and allows them to pass this ownership on to the next of kin, say their children, and they can profit from owning them or simply keep others from profiting from their parent's work.
Copyright as a legal concept has been around for just over 300 years, and so as a body of law it is well established and reviewed by the courts.
A copyright is a legal mechanism by which people can protect their ideas and save the work they have created from being used by other to make monetary gains, usually at the expense of the original creator. For works created before 1978, copyrights lasted for 70 years after the death of the creator of the work. In case the work was created by employees for a firm and all rights of the work were transferred to the firm, the firm had an exclusive right to it for 95 years after it was published, or for 120 years after the work was created. Anything created before 1923 is considered in the public domain and can be used by anyone.