This is a quote from the book "The ​Virtue Of Selfishness" by Ayn Rand
...ncepts have a hierarchical structure. The foundation and starting point of man’s thinking are his sensory perceptions; on this base, man forms his first concepts, then goes on building the edi fice of his knowledge by identifying and integrating new concepts on a wider and wider scale. If man’s thinking is to be valid, this process must be guided by logic, “the art of noncontradic tory identification” — and any new concept man forms must be integrated without contradiction into the hierarchical structure of his knowledge. To introduce into one ’s consciousness any i...
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