reason as his only absolute". She considered Objectivism a systematic philosophy and laid out positions on metaphysics, aesthetics, epistemology, ethics, and political philosophy. Metaphysics and epistemology In metaphysics, Rand supported philosophical realism and opposed anything she regarded as mysticism or supernaturalism, including all forms of religion. Rand believed in free will as a form of agent causation and rejected determinism. In aesthetics, Rand defined art as a "selective re-creation of reality according to an artist's metaphysical value-judgments". According to her, art allows philosophical concepts to be presented in a concrete form that can be grasped easily, thereby fulfilling a need of human consciousness. As a writer, the art form Rand focused on most closely was literature. She considered romanticism to be the approach that most accurately reflected the existence of human free will. In epistemology, Rand considered all knowledge to be based on sense perception, the validity of which she considered axiomatic, and reason, which she described as "the faculty that identifies and integrates the material provided by man's senses". Rand rejected all claims of non-perceptual knowledge, including instinct,' 'intuition,' 'revelation,' or any form of 'just knowing. In her Introduction to Objectivist Epistemology, Rand presented a theory of concept formation and rejected the analytic–synthetic dichotomy. She believed epistemology was a foundational branch of philosophy and considered the advocacy of reason to be the single most significant aspect of her philosophy. Commentators, including Hazel Barnes, Nathaniel Branden, and Albert Ellis, have criticized Rand's focus on the importance of reason. Barnes and Ellis said Rand was too dismissive of emotion and failed to recognize its importance in human life. Branden said Rand's emphasis on reason led her to denigrate emotions and create unrealistic expectations of how consistently rational human beings should be. Ethics and politics In ethics, Rand argued for rational and ethical egoism (rational self-interest), as the guiding moral principle. She said the individual should "exist for his own sake, neither sacrificing himself to others nor sacrificing others to himself". Rand referred to egoism as "the virtue of selfishness" in her book of that title. In it, she presented her solution to the is–ought problem by describing a meta-ethical theory that based morality in the needs of "man's survival qua man". She condemned ethical altruism as incompatible with the requirements of human life and happiness, and held the initiation of force was evil and irrational, writing in Atlas Shrugged that, "Force