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I have modified the source code of an MIT licensed project, and I have added new classes to it as well. Please correct me if I am wrong, but I think that it is legal to add my copyright notice above the license and remove the other one. But how should I attribute the contribution of the previous authors? Should I use a separate file? There are also some HTML files with no license or copyright notice in them which I also modified. Do I have to handle them differently?

My question is different than this question in that I have also modified some of the files of the project I am extending.

Update

Although the suggestion to remove the copyright notice sounds weird, what I had in mind when I first posted this, is that the authors should not be responsible if I add something malicious to their code. This should not be a problem since MIT license includes a disclaimer.

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    The original license still applies to your modifications. I wouldn't appreciate somebody making modifications to something I published then decides to replace the copyright notice. The original notice still applies. The question's answer you linked applies to your question.
    – Ramhound
    Commented Dec 4, 2012 at 12:25
  • So the answer is to keep the copyright notice but how do I indicate that the code was modified? Can I add my name-organisation next to the copyright? Of course I am going to keep the license in the modified code
    – kon psych
    Commented Dec 4, 2012 at 12:43
  • Just add your own copyright notice? The original copyright and MIT license applies to your code, doesn't matter if you modify the existing code, the entire library ( present and future ) is licensed.
    – Ramhound
    Commented Dec 4, 2012 at 12:49

3 Answers 3

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I am not a lawyer, but according to the MIT license:

The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software.

Therefore you may not remove the existing copyright notice. You may only add your copyright notice and license terms to portions of code that you own the copyright to, which are your new or modified code.

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    Your answer was helpful although it is not clear to me how I will add my copyright notice to modified code. I will probably include it in the Javadoc of my functions but I cannot and it does not worth to document every line I changed.
    – kon psych
    Commented Dec 4, 2012 at 14:49
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    It's not clear to me either! Most people would not bother to document every line they changed. I suppose if it ever came down to a legal issue you would just diff the other project with your project.
    – sourcenouveau
    Commented Dec 4, 2012 at 17:08
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I am not a layer, but here is what I proposed and was validated in my jurisdiction:

  • Include ALL license files from any included MIT code, be it forked, copied as-is, etc.
  • If the license files are copied, or renamed (to avoid overwrites), you can name them LICENSE- (e.g. LICENSE-numpy).
  • Create a main LICENSE that is your license, and at the end of the file you list all the MIT software along with their copyright holders, and the relative path to the related license file.
Flux Capacitor 1.0
Copyright (c) 2020 ACME Corporation, all rights reserved. Yada, yada, yada...

Includes other software related under the MIT license:
- Soft1, Copyright 2013 John Doe. For licensing see /LICENSE/LICENSE-soft1.txt
- Soft2, Copyright 2010 Mary Smith. For licensing see /LICENSE/LICENSE-soft2.txt
- Soft3, Copyright 2010 Dr Elwood. For licensing see /SOFT3/LICENSE.txt

Ideally, you would leave the license files in each software/package directory with the original file name (as in the example of Soft3 above), but that is not always possible, particularly when merging a lot of code form different authors into a whole new product. For Soft1 and Soft2, I moved the license files to /LICENSE directory instead. These are just examples and in real life I would strive to keep a convention across all license files.

According to my legal council, it is perfectly valid to rename or move the license files, if this was done in order to provide further clarity on what is what.

Consider for example, software that isn't redistributed, but has some sort of about box. They could have a section that says:

Portions of this software are copyright of their respective authors and released
under the MIT license:
- Soft 1, Copyright 2013 John Doe
- Soft 2, Copyright 2010 Mary Smith
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    Quite petty to down-vote a perfectly acceptable answer without providing any comments. This is the solution we have adopted in my organisation which was validated by our own legal team AND by 3rd parties.
    – pmdci
    Commented Jul 18, 2020 at 1:17
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    A practical example of how this has to be handled was exactly what I was looking for(rather than people giving their opinion, if including or removing a license is legal or not and that's not what the OP had asked, the OP had asked how the licenses should be included). People who downvoted, please enlighten us why this answer is not valid.
    – lordvcs
    Commented Oct 27, 2020 at 8:00
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Please correct me if I am wrong, but I think that it is legal to add my copyright notice above the license and remove the other one.

You cannot delete the original copyright notice. That's out-and-out illegal.

Whether you can add your own notice is a bit dicey, and I am not a lawyer. What you have created falls into the category of "Derivative Works."

From US Copyright Office Circular 14: Derivative Works:

To be copyrightable, a derivative work must be different enough from the original to be regarded as a "new work" or must contain a substantial amount of new material. Making minor changes or additions of little substance to a preexisting work will not qualify the work as a new version for copyright purposes. The new material must be original and copyrightable in itself. Titles, short phrases, and format, for example, are not copyrightable.

If your changes do constitute copyrightable material, your copyright only pertains to your contributions. It does not pertain to the preexisting material.

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    So if there is just one license.txt is it appropriate to add the names of the contributors under the original author in that one file
    – user82793
    Commented Sep 17, 2013 at 15:13

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