The second sense of "obscurantism" denotes making knowledge abstruse, that is, difficult to grasp. In the 19th and 20th centuries obscurantism became a polemical term for accusing an author of deliberately writing obscurely, in order to hide his or her intellectual vacuousness. Philosophers who are neither empiricists nor positivists often are considered obscurantists when describing the abstract concepts of their disciplines. For philosophic reasons, such authors might modify or reject verifiability, falsifiability, and logical non-contradiction. From that perspective, obscure (clouded, vague, abstruse) writing does not necessarily indicate that the writer has a poor grasp of the subject, because unintelligible writing sometimes is purposeful and philosophically considered. In contemporary discussions of virtue ethics, Aristotle's "Nicomachean Ethics" ("The Ethics") stands accused of ethical obscurantism, because of the technical, philosophic language and writing style, and their purpose being the education of a cultured governing elite. Immanuel Kant employed technical terms that were not commonly understood by the layman. Arthur Schopenhauer contended that post-Kantian philosophers such as Johann Gottlieb Fichte, Friedrich Wilhelm Joseph Schelling, and Georg Wilhelm Friedrich Hegel deliberately imitated the abstruse style of writing practiced by Kant. Hegel's philosophy, and the philosophies of those he influenced, especially Karl Marx, have been accused of obscurantism. Analytic and positivistic philosophers, such as A. J. Ayer, Bertrand Russell, and the critical-rationalist Karl Popper, accused Hegel and Hegelianism of being obscure. About Hegel's philosophy, Schopenhauer wrote that it is: "... a colossal piece of mystification, which will yet provide posterity with an inexhaustible theme for laughter at our times, that it is a pseudo-philosophy paralyzing all mental powers, stifling all real thinking, and, by the most outrageous misuse of language, putting in its place the hollowest, most senseless, thoughtless, and, as is confirmed by its success, most stupefying verbiage. ..." Nevertheless, biographer Terry Pinkard notes "Hegel has refused to go away, even in analytic philosophy, itself." Hegel was aware of his obscurantism, and perceived it as part of philosophical thinking: to accept and transcend the limitations of quotidian (everyday) thought and its concepts.