An art work does not formulate the metaphysics it represents; it does not (or at least need not) articulate definitions and principles. So art by itself is not enough in this context. But the point is that philosophy is not enough, either. Philosophy by itself cannot satisfy man's need of philosophy. Man requires the union of the two: philosophy and art, the broad identifications and their concrete embodiment. Then, in regard to his fundamental, guiding orientation, he combines the power of mind and of body, i.e., he combines the range of abstract thought with the irresistible immediacy of sense perception.
Ayn Rand summarizes in a definitive formulation:
Art is a concretization of metaphysics. Art brings man's concepts to the perceptual level of his consciousness and allows him to grasp them directly, as if they were percepts.
This is the psycho-epistemological function of art and the reason of its importance in man's life (and the crux of the Objectivist esthetics).
Here again we see man's need of unit-economy. Concepts condense percepts; philosophy, as the science of the broadest integrations, condenses concepts; and art then condenses philosophy—by returning to the perceptual level, this time in a form impregnated with a profound abstract meaning.
There is an obvious analogy here between language and art. Both blend parts (whether perceptual units or philosophical principles) into a whole by similar means: both complete a process of conceptual integration by the use of sensuous elements. Both thereby convert abstractions into the equivalent of concretes. As Miss Rand puts it, both convert abstractions "into specific entities open to man's direct perception. The claim that 'art is a universal language' is not an empty metaphor, it is literally true—in the sense of the psycho-epistemological function performed by art."
("Psycho-epistemology" is an invaluable term of Ayn Rand's, albeit one that pertains more to psychology than to philosophy. "Psycho-epistemology" designates "the study of man's cognitive processes from the aspect of the interaction between the conscious mind and the automatic functions of the subconscious." Epistemology, in essence, studies conscious, volitional processes; a "psycho-epistemological" method or function is one that also involves subconscious, automatized elements.)
By converting abstractions into percepts, art performs another crucial (and inseparable) function. It not only integrates metaphysics, but also objectifies it. This means: it enables man to contemplate his view of the world in the form of an existential object—to contemplate it not as a content of his consciousness, but "out there," as an external fact. Since abstractions as such do not exist, there is no other way to make one's metaphysical abstractions fully real to oneself (or, therefore, fully operative as one's guide). "To acquire the full, persuasive, irresistible power of reality," Miss Rand writes, "man's metaphysical abstractions have to confront him in the form of concretes—i.e., in the form of art."
Dr. Leonard Peikoff, "Objectivism: The Philosophy of Ayn Rand", p. 418-419.