I wish we could consider different terms for the different aspects of copyright. Copyright is not a single right--it is a bundle of rights. In the US (whose law I will use for all of this comment), for instance, it includes:<p>• The rights to make and distribute copies,<p>• The rights to make and distribute derivative works,<p>• The rights to publicly perform and display works.<p>The power to even have Federal copyright law comes from this grant of power in the Constitution:<p><pre><code> To promote the Progress of Science and useful Arts, by securing
for limited Times to Authors and Inventors the exclusive Right
to their respective Writings and Discoveries.
</code></pre>
That gives a purpose for the power (promoting science--which is used in its archaic meaning, which means knowledge, rather than its modern meaning, which is what once was called natural philosophy), and also the mechanism by which it is to be exercised (giving authors a limited monopoly).<p>Shorter terms promote progress by making works more widely available, but longer terms ALSO promote progress by letting authors make more money which improves things on the supply side, so setting the term requires balancing these, and I see no reason that the optimal setting for, say, copying should be expected to be the same as the optimal setting for, say, making derivative works.<p>I also see no reason the term needs to be the same for different types of works. Music, literature, movies, and computer software are very different so why would we expect that a term that is good for music when it comes to balancing wide distribution vs. author incentive to also be good for literature, moves, and software?