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The act of isolation involved [in concept-formation] is a process of abstraction : i.e., a selective mental focus that takes out or separates a certain aspect of reality from all others (e.g., isolates a certain attribute from the entities possessing it, or a certain action from the entities performing it, etc.).

Concept Formation,
Introduction to Objectivist Epistemology, 10

The higher animals are able to perceive entities, motions, attributes, and certain numbers of entities. But what an animal cannot perform is the process of abstractionof mentally separating attributes, motions or numbers from entities. It has been said that an animal can perceive two oranges or two potatoes, but cannot grasp the concept two.

Concept Formation,
Introduction to Objectivist Epistemology, 16

Acknowledgments

Excerpts from The Ominous Parallels, by Leonard Peikoff. Copyright 1982 by Leonard Peikoff. Reprinted with permission of Stein and Day Publishers. Excerpts from The Romantic Manifesto, by Ayn Rand. Copyright 1971, by The Objectivist. Reprinted with permission of Harper & Row, Publishers, Inc. Excerpts from Atlas Shrugged, copyright 1957 by Ayn Rand, The Fountainhead, copyright 1943 by Ayn Rand, and For the New Intellectual, copyright 1961 by Ayn Rand. Reprinted by permission of the Estate of Ayn Rand. Excerpts from Philosophy: Who Needs It, by Ayn Rand. Copyright 1982 by Leonard Peikoff, Executor, Estate of Ayn Rand. Reprinted by permission of the Estate of Ayn Rand. Excerpts from The Philosophy of Objectivism lecture series. Copyright 1976 by Leonard Peikoff. Reprinted by permission. Excerpts from Alvin Tofflers interview with Ayn Rand, which first appeared in Playboy magazine. Copyright 1964. Reprinted by permission of Alvin Toffler. All rights reserved including the right of reproduction in whole or in part in any form. Used by arrangement with Plume, a member of Penguin Group (USA), Inc.