INTELLECTUAL, EDUCATIONAL, NEUROLOGICAL, PHYSIOLOGICAL, PSYCHOLOGICAL, AND SOCIOLOGICAL FACTORS IN VARIOUS PATTERNS OF INTERRELATIONSHIPS INFLUENCE THE THINKING PROCESS. INDIVIDUALS DIFFER IN THE CONCEPTS THEY HOLD AND IN THEIR USE OF THESE CONCEPTS BECAUSE OF VARIATIONS IN INTELLIGENCE AND BACKGROUND OF EXPERIENCE. THE RANGE AND LEVEL OF CONCEPTS THEY HAVE INFLUENCE THEIR REACTION TO SITUATIONS. HENCE, EXPERIENCE AND CONCEPT FORMATION PLAY FUNDAMENTAL ROLES IN THE DEVELOPMENT OF THINKING ABILITIES. THESE IN TURN ARE INFLUENCED BY THE PHYSICAL, EMOTIONAL, AND SOCIAL STATUS OF THE INDIVIDUAL. POOR HEALTH, NEUROLOGICAL INVOLVEMENT, AND EXTREME EMOTIONS HANDICAP THINKING ABILITIES. THE ENVIRONMENT AN INDIVIDUAL GROWS UP IN DEVELOPS IN HIM A PERSONALITY THAT MAKES HIM EITHER RECEPTIVE TO OR RESISTANT TO LEARNING. A FAVORABLE ENVIRONMENT PROVIDES FOR ORAL LANGUAGE DEVELOPMENT AND ENCOURAGES INDEPENDENT THOUGHT AND ACTION. NONE OF THE FACTORS MENTIONED WILL SERIOUSLY AFFECT THINKING ABILITIES UNLESS THEY OPERATE TOGETHER OR CONTRIBUTE TO ONE ANOTHER. THIS PAPER IS PUBLISHED IN "READING AND THINKING, PROCEEDINGS OF THE 22ND ANNUAL READING INSTITUTE AT TEMPLE UNIVERSITY," TEMPLE UNIVERSITY, PHILADELPHIA, PA., 1965. (NS)