My intent was not to start an argument over semantics nor over anything else. I merely intended to clarify where I think some imprecision and unnecessary disagreement has entered the thread. If we keep using words we define differently as a basis, then we at least need to know how those words are being used by each party. Otherwise we'll talk past one another and nobody really knows where we would agree and disagree no matter how civil or friendly the discussion.
I also think it helps to remember that intentions toward a project can change over time. What one thinks will be a straightforward rewrite from the beginning can change in focus and gain features before the rewrite is done (or even really started). The new design can be a totally different sort of beast from the old, but since it's still in the same lineage the distinction is blurred. In fact, I suspect that the svn folks intended to rewrite CVS but looking back would only loosely use that term for what they finally did. I think Larry would say Perl 5 is a rewrite of Perl 4 from the point of view of both the language and the perl tool. I would probably say that, anyway. I think he intended originally for Perl 6 to be a rewrite of some sort, but the language is the only thing being rewritten IMO. I think Rakudo and Parrot are definitely not rewrites of perl 5.6 or 5.8 although the language implemented is still in the Perl family. How Larry actually does view things of course would be for Larry to say no matter what I think he might say.