The philosophy of Epicurus was actually a philosophical hybrid and it came about as the result of a combination of the Atomism of Democritus and the Hedonism of Aristippus. Epicurus formulated a new doctrine from the pleasure-loving individualistic Greeks of the Asiatic coast, designed for the use of the educated upper and middle classes of the Athenian mainland. It was a philosophy of detachment and impeccable taste, and unlike stoicism, it was never meant to appeal or to apply to the masses, or to the universal state.

Epicureans were very unpopular as a movement in Greece though, because their teachings ran completely counter to the Stoics, Platonists and Aristotelians of their day, although they were more accepted in the Roman world at a later day. Unlike the Stoics, Platonists or Aristotelians, the Epicureans did not unduly affect Christianity. But like the Stoics however, the Epicurean philosophy was divided into three main parts:
• Canonics
• Physics
• Ethics

Their prime rule of life was based on reason, but reason tempered with ataraxia, upper tranquility. They denied any Divine Power in their affairs and tranquillity in their eyes equaled freedom from pain and from fear and desire. Their basic equation was Happiness = Pleasure – Pain.

That is not the case. A righteous solider fighting for his reasonable cause, may be suffering physical trauma as pain, but he will be happy. A farmer, working hard sweating allot at his farm, may not be free of pain, but his sense of completing his own chosen worthy task will cause him happiness.
A woman going to be a mother, feeling the labor pains, will surely be happy for the hard work she is constantly doing to create, nourish, and safeguard the life within her womb.
Happiness can be Pleasure-Pain; Happiness can be Pleasure+Pain…
Nevertheless, Happiness will always be Righteous on the base of reason! Happiness cannot be Unreasonable.
However, the equation Happiness=Pleasure-Pain, is not a vague statement. It is a valid reason by virtue of which, the human always tries honestly and progressively to reduce and deny the pain.
It is for this cause for which medical science revolves around easement and cure of pain.

Pain is a strictly informing signal by the neuron-system to the mind, that there is some default, or problem within the perfect body system. And that default needs to be looked after and cured/cared about.
How will a person come to know that what he is doing is righteous or wrong?
The facility to experience pleasure or pain is inherent in a human’s body; it is an essential element of his character. He has no alternative on the subject of it, and he has no choice about the standard that determines what will make him experience the physical sensation of pleasure or of pain. What standard he has then, His own Life, His existence.
The pleasure-pain system in the body of human or in the bodies of any living being, which have the sense of realization, serves as an mechanical sentinel of the living being’s existence. The physical consciousness of pleasure is a pointer demonstrating that the existing being is pursuing the right course of action. The physical sensation of pain is a warning signal of danger, indicating that the being is pursuing the wrong course of action, that something is impairing the proper function of its body, which requires action to correct it.
This natural mechanism of pleasure and pain is very essential for any living being or human to actually realize the reasons and hence reality and course of right and wrong.
The example of mentally retarded children can explain it very precisely, who are born with a deficiency of such practical innate mechanical system of learning. Such children have no means of learning that what can and will injure them. The survival chances of such children are always less. The question of the possibility of a living being without having any of the five innate senses also depends on this.
The righteous sado-masochistic psychological relation also uses this imperative method for the actual pleasure, happiness, progress and emotional creativity.
When we talk of creativity, I remember of Plato.
Plato was wrong when he said since there is no perfect circle in universe hence there must be reincarnation and we might have observed a perfect circle some where in other universe in some previous birth. Mind do not need rebirth to experience a perfect circle.
Mind can create a circle to perfection.
Imagination should be reasonable. Now Jules Verne explained the idea of submarines at a time when there was no submarine. First submarine took its shape after 100 years of Jules death. It does not mean that Verne saw some submarine in some other universe, but there was some rational in the idea of Jules submarine. Hence, the men tried to achieve that rationale, and made the submarine possible. if I imagine a god or an angel, it wont become reality. Imagination must be reasonable. Therefore, perfect circle is a reasonable imagination. Mathematics defines it. Definition is creation in itself. The virtual picture of perfect circle on computer based on definition is creation; on the sheet by use of divider is creation. Nature do not provides anything except mind, man uses mind to extract or create, discover or invent.
What is the defining attribute of humanity? What has brought us this far?
our need and basic reason, to enjoy our existence. To be happy is the moral purpose of your life.
Only that moral purpose forces us to define create, and reasoning things.