When we talk about famous Greek personalities, we can't afford to miss out on Socrates―the ancient Athenian philosopher, who taught people 'how to think'. During his times, the task of inculcating critical thinking in the society was way more difficult than what it is today.
Those who occupied the high positions in society were least impressed by Socrates' efforts, as his philosophy questioned the very attributes on which the society was standing tall.
Eventually, Athenians charged Socrates with impiousness, i.e., the lack of respect for God, and corrupting the minds of youth, which were back then considered very serious offenses, and sentenced him to death.
That, however, was too late, as Socrates' philosophy had already been rooted in people's minds. In course of time, his students ensured that his preachings reached everybody through their writings.
Socratic Method (A.K.A. Method of Elenchus)
The Socratic Method, also referred to as the method of "elenchus", is by far Socrates' most important contribution to philosophy. It revolved around the basic concept of facilitating discussion by posing a particular question to a group of people, and identifying and eliminating all the contradictory hypothesis to find the most suitable hypothesis.
Socrates resorted to this method to question some of the basic attributes of society, including justice, good and bad, beauty, wisdom, etc. Soon, he had a group of youngsters, including Plato, Aristophanes, and Xenophon, who were eager to listen to him. Interestingly, most of our knowledge about his philosophy can be attributed to their literary works.
Socrates' Philosophies on Various Attributes of Life
Socrates lived by the motto 'know thyself', as he was of the firm belief that an unexamined life was not a life worth living. He introduced the concept of 'good life' to the world, wherein the person's way of living was characterized by thoughtfulness and critical appreciation.
He defined good life as a life which was always guided by an inquiring and expanding mind. Socrates was strictly against the practice of following the primal instincts and old customs as a way of life in the guise of piousness.
Socrates divided knowledge into two types: ordinary knowledge, i.e., specific knowledge which was not of much worth for the possessor, and higher knowledge, which involved the definition of words and concepts which were helpful in the quest for truth.
His idea of education included interpretation of statements, examination of knowledge, learning from wise people, examining oneself as well as others, and attaining moral knowledge. Interestingly, Socrates also believed that our quest for truth was blurred by our pursuit of any specific discipline.
Socrates was of the opinion that love which we develop for 'beauty' can never be satisfied, until we die, and therefore, one should go beyond the outer stimulating image that can be seen and contemplate beauty in itself.
According to the Socratic version, love was an epiphenomenal entity, which was generated by our physical actions, but seldom grasped by our mind or language.
He believed that there was no point in being afraid of some unknown concept such as death. He was of the opinion that death may either be deep sleep, wherein the person experiences complete relaxation of body and mind, or transmigration of soul from one body to another.
Owing to the fact that none of these philosophic principles were documented by Socrates himself, we have to rely on the information provided in the secondary sources, such as the writings of his students.
Add to it the fact that these literary works are interpreted by different people in different ways, it becomes all the more difficult to ascertain the facts. So you shouldn't be surprised if you come across different sources giving different explanations about the philosophical principles followed by him.