Born 341 BCE, seven years after the death of Plato, Epicurus was a prominent milestone in the Greek tradition of thought. His philosophy was yet another independent system which sought to reach the level of the accounts of reality and the purpose of humanity given by those such as Plato and Aristotle. He founded The Garden in Athens, a philosophical school and community, which sought to put his teachings into action. Like many of the Greek philosophers of this time period, very little of his work remains. Even more so for Epicurus, as his ideas were suppressed by the rise of Christianity. Luckily Diogenes Laertius, a biographer for ancient Greek philosophers, published three letters supposed written by Epicurus, which create much of the foundation for our understanding of his beliefs.
The ethics of Epicurus are elegantly simple, and serve as a sort of distillation of the ethics of Socrates and Aristotle. It goes as follows. Philosophy is necessary for the health of the soul, thus it must be a lifelong practice. Aside from that, practice whatever it is that gives you happiness. All good and bad is contained within sense experience, so the maximization of positive sensory experience is the key to happiness. Do not fear death, as it is simply the lack of sensory experience, and thus is neither good nor bad. "The wise man neither rejects life nor fears death." This type of ethical belief system is now commonly referred to as Hedonism. Epicurus's happiness is much simpler and easier to obtain then the happiness discussed by Aristotle, which makes it a much more realistic goal for normal people. This is probably why is became so popular during the Hellenistic period.
I myself am more impressed with some of Epicurus's views on science and human nature. He describes the universe as being composed of space and bodies. Though he did know know about the distinction between particles and waves, nor about the relationship between space and time, he made some very admirable attempts to describe the universe, including attempts at describing gravity and statements that are very similar to Newton's first law of motion. He even made statements that pointed to a belief in the biological evolution of human consciousness and language. "...we must suppose that human nature too was taught and constrained to do many things of every kind merely by circumstances; and that later on reasoning elaborated what had been suggested by nature and made further inventions..." "And so names too were not at first deliberately given to things, but men’s natures according to their different nationalities had their own peculiar feelings and received their peculiar impressions, and so each in their own way emitted air formed into shape by each of these feelings and impressions..."
One of Epicurus's most interesting claims, and one that surely got him in trouble with early Christianity, was that we must not believe that the movements of heavenly bodies are being controlled by gods, but that their movements are an established and intrinsic part of the universe. With this in mind we must also never downplay the majestic significance of these heavenly bodies, for such a contradiction would cause a great disturbance within the soul. Epicurus's ideas on the soul are rather unique. He believed that the soul is a physical object that is spread throughout the body, the presence of which is responsible for our ability to perceive. When we die, our soul leaves our body and sensation ceases. This type of materialist soul theory is uncommon. Most theories about human consciousness are either dualist and contend that the soul is a non-physical object, or are materialist and contend that the soul can only exist within a living body or that souls do not exist at all. It is perhaps because of his materialist view of the soul that Epicurus repeatedly sought to disprove the concept of the immortal soul.
If I were to level any one criticism at the philosophy of Epicurus it would be that it is naive. Epicurus trusts too greatly in the accuracy of human perception and the nobility of the human search for knowledge. "...we must believe that to discover accurately the cause of the most essential facts is the function of the science of nature..." Science is nothing more than the human search for knowledge. As it is a function of humanity, science is always at risk of being tainted by human intention and bias. The results of an experiment can never truly be verified until they have been replicated by a different scientist. Thus the discovery of knowledge about the universe is the purpose of science, but not always it's function.
More Ancient Greek Philosophers:
Part 1 - Thales of Miletus
Part 2 - Heraclitus of Ephesus
Part 3 - Pythagoras of Samos
Part 4 - Parmenides and Zeno of Elea
Part 5 - Socrates
Part 6 - Plato
Part 7 - Aristotle