Excerpt from Atlas Shrugged by Ayn Rand (as quoted from the character, John Galt):
"Are you seeking to know what is wrong with the world? All the disasters that have wrecked your world, came from your leaders’ attempt to evade the fact that A is A. All the secret evil you dread to face within you and all the pain you have ever endured, came from your own attempt to evade the fact that A is A. The purpose of those who taught you to evade it was to make you forget that Man is Man.
"Man cannot survive except by gaining knowledge, and reason is his only means to gain it. Reason is the faculty that perceives, identifies and integrates the material provided by his senses. The task of his senses is to give him the evidence of existence, but the task of identifying it belongs to his reason; his senses tell him only that something is, but what it is must be learned by his mind.
"All thinking is a process of identification and integration. Man perceives a blob of color; by integrating the evidence of his sight and he touch, he learns to identify it as a solid object; he learns to identify the object as a table; he learns that the table is made of wood; he learns that the wood consists of cells, that the cells consist of molecules, that the molecules consist of atoms. All through this process, the work of his mind consists of answers to a single question: What is it? His means to establish the truth of his answers is logic, and logic rests on the axiom that existence exists. Logic is the art of non-contradictory identification. A contradiction cannot exist. An atom is itself, and so is the universe; neither can contradict its own identity, nor can a part contradict the whole. No concept man forms is valid unless he integrates it without contradiction into the total sum of his knowledge. To arrive at a contradiction is to confess an error in one’s thinking; to maintain a contradiction is to abdicate one’s mind and to evict oneself from the realm of reality.
"Reality is that which exists; the unreal does not exist; the unreal is merely that negation of existence which is the content of a human consciousness when it attempts to abandon reason. Truth is the recognition of reality; reason, man’s only means of knowledge, is his only standard of truth.
"The most depraved sentence you can now utter is: Whose reason? The answer is: Yours. No matter how vast your knowledge, or how modest, it is your own mind that has to acquire it. It is only with your own knowledge that you can deal. It is only your own knowledge that you can claim to possess or ask others to consider. Your mind is your only judge of truth—and if others dissent from your verdict, reality is the court of final appeal. Nothing but a man’s mind can perform that complex, delicate, crucial process of identification, which is thinking. Nothing can direct the process but his own judgment. Nothing can direct his judgment but his moral integrity."