Answer: "I am not primarily an advocate of capitalism, but of egoism; and I am not primarily an advocate of egoism, but of reason. If one recognizes the supremacy of reason and applies it consistently, all the rest follows." ( Ayn Rand , "Introducing Objectivism ," The Objectivist Newsletter Vol. 1 No. 8, August 1962, p. 35)
Philosophies are systems of ideas because their theories are connected in a hierarchy. Beginning with the most fundamental issues, the conclusions one reaches in one field of philosophy have profound implications about what one can consistently conclude in another.
Metaphysics is the most basic field. It tells you what reality is, which obviously sets the terms for other fields. If the world we see is an illusion, as the Buddhists teach, then epistemology must explain how we acquire knowledge by some means other than sense perception. And if there is an afterlife, and an eternal reward awaiting us in heaven or hell, as the Christians teach, then ethically we ought to do whatever we can to reach eternal bliss.
Epistemology is also basic in a different respect. All our theories and ideas depend on the standards we have for knowledge. We cannot have ethical, political, or aesthetic knowledge except by the terms set by epistemology. Religions depend on being able to appeal to faith as a basis for knowledge of ultimate reality.
Ethics establishes the difference between right and wrong. Its positions depend on a view of reality, on facts about human nature, and on the standards of knowledge. It establishes a code of values and explains the difference between virtue and vice. This provides basic and fundamental guidance for human choices, including the paths we take in our own lives, what we expect from others, and the direction of institutions and even whole cultures. All areas of human endeavor depend on ethical premises about what is valuable and what purposes are worthy.
Aesthetics depends on ethics because ethics establishes what are valid human needs and what is good for humans as opposed to the bad. These are premises that any explanation of the value and standards of art must employ.
Politics depends on ethics because ethics sets the goals of government and the aims, more generally, of social organization.
A philosophy that does not address all the major issues is incomplete. A philosophy that is inconsistent in its positions is indefensible. We can see the importance of consistency by seeing how the lack of it affects political ideologies.
Most American conservatives, for example, are Christians who attempt to be champions of industry and the free market, while advocating for their religion at the same time. But as most Americans sense, the two are not consistent. Jesus, after all, taught that the rich should give away all their possessions. And the core Christian virtues of faith, hope, and charity suit a St. Francis far better than a Bill Gates. So conservatives are torn between the two tendencies of Christianity and capitalism. Some, choosing capitalism, emphasize American traditions of freedom, local government, and tolerance. Others, choosing Christianity, attack our "materialist" culture, advocate paternalistic government programs like welfare, and push for greater government support for religion.
American liberals, for their part, are torn between valuing freedom and personal happiness (which they advocate in regard to freedom of speech and abortion rights) and valuing equality (which they seek to promote through codes that restrict choice and restrain speech, such as the laws banning racial discrimination or sexual innuendo in private business contexts).
Many formal philosophies suffer from similar contradictions. Immanuel Kant, for example, was an advocate of political freedom and peace, but his followers often supported dictatorships and war, because they tried to live by his morality of pure adherence to duty.
is a full system of thought that stakes out positions in all the major fields of philosophy. It is a consistent system of thought in which each position is supported by more basic positions beneath it and supports derivative positions that follow from it. Objectivists find that what they know about one field of philosophy supports what they know about the others, so they do not have to choose between contradictory tendencies as modern conservatives and liberals do. And their conclusions, being based in the facts, follow logically from the most basic ideas to the most derivative.