I didn't like the intentionality that he had in his definition, but it was good that he included the arts here, and I really liked the phrase "Anschein eigenen Schaffens" (the appearance of own work).
“Plagiat ist also die aus freier Entschließung eines Autors oder Künstlers betätigte Entnahme eines nicht unbeträchtlichen Gedanken inhalts eines anderen für sein Werk in der Absicht, solche Zwangsanleihe nach ihrer Herkunft durch entsprechende Umgestaltung zu verwischen und den Anschein eigenen Schaffens damit beim Leser oder Beschauer zu erwecken.” [S. 81-82]
As it turns out, Paul English was himself accused of plagiarism. In 1908 a Viennese author, Dr. Stern-Szana, prepared a handwritten manuscript for a book. It was purchased in 1920 by a publisher in Berlin, Socher. In 1922 Socher gave the manuscript to a typist to have it prepared for publication. The typist was Paul English. The book, however, was never published by Socher. But in 1928 Paul English published a book with the exact same title and extremely similar structure, as well as occasional word-for-word copies.
Socher took English to court in 1929 and there is a wonderful book (that has now been digitized) that Socher put together for the court case, a side-by-side of English and Stern-Szana's manuscript. English republished his book with a new title, the contents unchanged. The court case seems to have gone on to a higher court in 1932, the trail is lost there. I will be researching this during my sabbatical in the hopes that the result of the case has not been lost in the destruction wreaked by the Second World War in Germany. If anyone happens on a clue, please contact me.
A booklet with the definition by English was first published as "Plagiat!! Plagiat!!" in 1930, and then in an extended version as "Meister des Plagiats - oder die Kunst der Abschriftstellerei" in 1933. With the knowledge of the history of English and the context from page 81 of the latter publication, I now read his "definition" as an attempt to wash his hands of the taint of plagiarism. I have now removed the definition from my plagiarism portal and from my slides. I now use Teddi Fishman's definition. I apologize for any inconvenience.