Cover Page -- Title Page -- Copyright Page -- Table of Contents -- Preface -- 1. INTRODUCTION -- 1. A Distinction -- 2. Some Other Studies in Light of the Distinction -- 3. Qualification and Clarifications of the Distinction -- 2. EXPERIMENT I -- 1. Design -- 2. Subjects -- 3. Materials -- 4. Procedure -- 5. Preliminary Analyses of Results -- 6. Overview of Subsequent Data Analyses -- 3. CONSISTENCY -- 1. Interest of the Question -- 2. Pass Rates for Tasks in the Four Interpretations -- 3. Correlations between Interpretations -- 4. Consistency within Subjects -- 5. Relative Consistency of Successful and Unsuccessful Subjects -- 6. Implications of the Consistency Analyses -- 4. STANDARD LOGIC ALGORITHMS AS PSYCHOLOGICAL MODELS -- 1. Some Unsuccessful Attempts -- 2. Unsuitability of Standard Algorithms -- 5. A THEORY OF THE OPERATIONS UNDERLYING THE EXPERIMENTAL FORMULAS -- 1. The Operations -- 2. Context Restrictions for the Operations -- 3. Derivations of the Experimental Formulas -- 4. Eight Remarks about the Model -- 6. PERFORMANCE MODELS AND PREDICTION OF FORMULA DIFFICULTY -- 1. General Remarks -- 2. The First Performance Model -- 3. Weightings for the Operations -- 4. The First Performance Model, as Improved by Weightings -- 5. The Second Performance Model -- 6. Alternative Performance Models -- 7. A Noncumulative Performance Model -- 7. THE QUESTION OF THE LOCUS -- 1. Constraint on Hypotheses -- 2. A Theory Inconsistent with the Constraint on Hypotheses -- 3. Two Theories Consistent with the Constraint on Hypotheses -- 8. EXPERIMENT II -- 1. Design -- 2. Subjects -- 3. Materials and Procedure -- 4. Preliminary Analyses of Results -- 9. REPLICATION OF PREVIOUS ANALYSES -- 1. Consistency -- 2. Derivations for the Formulas of Experiment II -- 3. Prediction of Relative Difficulty of Formulas -- 4. The Question of Development Revisited