Plato contends that the good life is lived by fulfilling the natural function that all things possess. Plato believed that any object, animal or man has a natural function. Discovering that function is the first step in living the good life, and it is followed by acting on that function.
Since Plato's philosophy of the good life applies to all things, some functions are easier to discover and act upon than others. For example, a chair has a natural function to be sat upon. When it comes to mankind however, Plato felt that the natural function was more complicated, requiring that man live justly and achieve unity and harmony.
Plato felt that the soul of man had three parts, consisting of intellect, spirit and courage, and physical desires. Each part has its own need. However, to live the good life, the needs of each of the three parts of the soul must be met without interfering with the needs of the other two parts. These needs are basic ones. For example, the physical desires of the soul are fulfilled by good health and survival.
Reaching a level of balance is only the first step in living the good life. Plato felt that mankind's nature required more than simply existing in balance. Nature requires that an individual use intellect and reason to search for the truth, pursue further knowledge and seek ultimate reality.