This question has been raised and thoroughly discussed: "How to characterize the phrase, 'The ends justify the means.'" I wish to add a thought. As I was writing a book for publication, I came upon the same question about the phrase. Unlike the other previous answers in a well-thought-out thread, I concluded the phrase—based on the original question—is best described as a "proposition" since Machiavelli was a diplomat. The statement doesn't rise to a principal because it is debatable; however, it does spur an enduring (political and moral) discussion and is, therefore, a proposition.