The ‘real author’ isn’t the only injured party.
Copying from a book with a long dead author, or paying a willing confederate to write your thesis for you, is still plagiarism.
Copying from a book with a long dead author, or paying a willing confederate to write your thesis for you, is still plagiarism.
As a side note quite often it can actually be literal plagiarism as well, many journals require you to assign copyright, so using that work without attribution is plagiarism.