This thesis is of three main objectives:- (1) to study the development of the human beings based on the three ranges of age; i.e. Early age, Middle age and Last age, (2) to study the Buddhist principles, conforming to the development of human beings based on the three ranges of age, and (3) to apply the Buddhist principles to develop the human beings on the three ranges of age in Thai societies. This is a study of documents with the following results.

From the study, it is found that the human beings during early development are of the quickly physical and psychological changes by external factors such as family, society, culture, technology, communication and inventions as a catalyst for parents to take special training for the growth and the learning in the right direction. The middle-aged men are of the commitment to strengthen the family with social responsibility. When they are facing a problem, they can solve the problem. At the last age range, the human beings are of a physical impairment. Some families have problems and worries about being neglected. So, they must be both the physical and the mental care.

From the study of the Doctrinal principle which is in compliance with the human beings development, it is found that at the primary age, the parents must have some love, warmness, good relationship in the family, the understanding of the Doctrinal principles and the practice of themselves as the examples. More over, the parents must train their sons and daughter and must teach them to know what is suitable or unsuitable, useful or useless virtuous or non-virtuous. They also must teach their sons and daughters to know how use properly the outer factors what are influential to the children’s behaviors. At the middle age, it is to emphasize the matter of constructing the family, the carrying out of the family, the responsibility to the societies and the solving of the problems. In the final age, taking care of bodily and mental health must be emphasized by training themselves. More over, the sons and the daughters including the nephews must look after the old aged people closely. This is the good love, good warmth and good relationship.

Form the application of the Doctrinal principles to the Thai societies, it is found that the children have good knowledge in learning and developing their bodies and minds. It is the way to build up the state of protection and set up the base of stability in the next age. In the middle age, the Doctrinal principles help the people to build up the stability to the family, the occupation, the expenses, the responsibility to the societies, and solution of different problems. The application of the Doctrinal principle to the final age is the building up of the happiness to the old aged peoples’ worries about being abandoned and the being able to build up the state of being long aged people.