All twelve great economists made great contributions to economics, and all showed great enthusiasm in the study of economics. There were some differences between their concepts of economics, but all of these concepts built the basic ideas of economics that we study today. There were several criteria used to classify economists. First of all, the economist should have a great influence in economics. He/she should have substantive theories that could be applied in the real world and could be used as a reference for other economists. So he should enjoy his work in finding theories or developing his own ideas, he should show enthusiasm in studying economics. If he could appreciate his work, he would concentrate on the process of defining theories and ideas and give better results. Thus, significant and grand economic theories would be formed. Thirdly, he/she should devote himself to spreading the ideas of economics so that all people can receive the concepts of economics and thus improve the economy in the world. Spreading the ideas of economics was very important, others could make changes to his concepts and correct them. Finally, he should make a contribution to society. It was very important for the economist to consider public benefits when creating his own ideas that could have a great influence on society. Since economics is about the allocation of resources in the world, the economic theories created could influence the distribution of wealth in the world. Of the twelve great economists discussed in this course, I would rank Alfred Marshall first and Lerner Abba Potachya second. Economically, Alfred Marshall (1842-1924), the first economist I learned in this course, was the greatest economist among the twelve. He was just like the father of economics. He contributed much of his life to the economy. When he began teaching political economy at St John's College, he dedicated his career to developing the subject and helping to transform it into a new economic science. He spent several years developing and defining his economic ideas and deepening his understandings. He also visited the United States to survey economic conditions and throughout his life was tireless in his efforts to master the practical aspects of the economic world. It seems that much of his life was dedicated to economics.