Tough, A. M. (1979). The adult's learning projects: A fresh approach to theory and practice in adult learning (2d ed.). Learning Concepts.
توثيق أسلوب شيكاغو (الطبعة السابعة عشر)Tough, Allen M. The Adult's Learning Projects: A Fresh Approach to Theory and Practice in Adult Learning. 2d ed. Austin, Tex.: Learning Concepts, 1979.
توثيق جمعية اللغة المعاصرة MLA (الطبعة الثامنة)Tough, Allen M. The Adult's Learning Projects: A Fresh Approach to Theory and Practice in Adult Learning. 2d ed. Learning Concepts, 1979.
تحذير: قد لا تكون هذه الاستشهادات دائما دقيقة بنسبة 100%.