If I take a piece of software that is licensed as MIT (quoted at the end), and use it as a scaffold to create for my own thing, do I need to keep including the old license perpetually? This would seem ridiculous (although the law may see it differently), as I could potentially change (in actual meaning, rather than just rewriting the same logic but with different terms) every line of code and it would cease to have anything to do with the original author.
If I am correct, than at what point does the old author cease to retain copyright/the license ceases to hold?
In either case, at some points I would have made enough changes to warrant copyrighting them as well. How does one indicate which portions are under copyright by the old author and which are under mine?
I am interested mainly in answers from the perspective of US/common law. I understand that not all of these questions might have been tested in court, so a philosophical answer would suffice.
As a concrete example regarding which to test/explain, I would propose the "software" to be a style sheet for website. These are composed of relatively similar statements describing how different elements should look/behave (i.e. font size, font color, placement, etc., so if two people were to style the same element, there is a high probability that they would get at least some of the statements to coincide).
Finally, bonus points for explaining the relevant parts with regards to GPL(v2). I understand that it works differently as the license is supposed to be infectious, but copyright question still remains.
The MIT License (MIT) Copyright (c) <year> <copyright holders> Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files (the "Software"), to deal in the Software without restriction, including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is furnished to do so, subject to the following conditions: The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software. THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.