CONTENTS 



CHAPTER I. 



PAGE 



1 . Darwin's Theory of the Origin of Species 1 



2. Hyslop's Theory of a Life After Death 3 



3. Locke's Theory of Human Understanding 6 



4. The Theory of Ions 8 



5. The Theory of Inorganic Evolution 10 



6. The Theory that Matter is Electrical 11 



CHAPTER II. 



PAGE 

 Classification and Comparison of Theories 13 



CHAPTER III. 

 QUALITIES OF THEORIES 



PAGE 



1 . Believability of Theories 19 



2. Simplicity of Theories 21 



3. Verifiability of Theories 30 



4. Meaning of Truth of a Theory 35 



5. In what Sense do Theories Explain 36 



6. Usefulness of Theories 36 



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