Originally published: London : Kegan Paul, Trench, Trubner & Co., Ltd., 1924.

Foreword to the Routledge Classics Edition / Michael Rosenthal -- General Introduction -- Part 1: Basic Principles -- General Introductory Remarks on Fictional Constructs -- A. The Enumeration and Division of Scientific Fictions -- B. The Logical Theory of Scientific Fictions -- C. Contributions to the History and Theory of Fictions -- D. Consequences for the Theory of Knowledge -- Part 2: Amplified Study of Special Problems -- 1. Artificial Classification -- 2. Further Artificial Classifications -- 3. Adam Smith's Method in Political Economy -- 4. Bentham's Method in Political Science -- 5. Abstractive Fictional Methods in Physics and Psychology -- 6. Condillac's Imaginary Statue -- 7. Lotze's 'Hypothetical Animal' -- 8. Other Examples of Fictitious Isolation -- 9. The Fiction of Force -- 10. Matter and Materialism as Mental Accessories -- 11. Abstract Concepts as Fictions -- 12. General Ideas as Fictions -- 13. Summational, Nominal, and Substitutive Fictions -- 14. Natural Forces and Natural Laws as Fictions -- 15. Schematic Fictions -- 16. Illustrative Fictions -- 17. The Atomic Theory as a Fiction -- 18. Fictions in Mathematical Physics -- 19. The Fiction of Pure Absolute Space -- 20. Surface, Line, Point, etc., as Fictions -- 21. The Fiction of the Infinitely Small -- 22. The History of the Infinitesimal Fiction. -- 23. The Meaning of the' As If' Approach -- 24. The Fictive Judgment -- 25. The Fiction contrasted with the Hypothesis -- Part 3: Historical Confirmations -- A. Kant's Use of the 'As If' Method -- B. Forberg, The Originator of the Fichtean Atheism-Controversy, and his Religion of As-If -- C. Lange's 'Standpoint of the Ideal' -- D. Nietzsche and his Doctrine of Conscious Illusion -- Index.