"All virtue is summed up in dealing justly."
Aristotle was educated at Plato's academy from the age of 17 and lived and worked there for 20 years, until Plato's death. After years of travel and study, including teaching Alexander the Great, he returned to Athens and founded his own academy, the Lyceum or peripatetic school. He developed his own philosophical views, which often differed from those of Plato. For example, Aristotle claimed that the world of perceived things is the real world and that there are no perfect forms in a realm beyond.
Aristotle understood the importance of observation in scientific enquiry and wrote much about cause and effect in nature (especially his theory of four causes in the Physics). His writings covered biology, animal behaviour, the weather, planetary motions, stars and Gods as well as politics and ethics.
"Moral excellence comes about as a result of habit. We become just by doing just acts, temperate by doing temperate acts, brave by doing brave acts. "
Aristotle believed that behaving in a just manor and making a habit of it will ultimately result in moral excellence. He also warned against extreme behavior. He espoused the doctrine of 'the golden mean', also shared independently by Confucius, that is, the best path in life is the one between two extremes. For example, the virtue of truthfulness consists of choosing the mean between boasting and undue modesty. The mean varies depending upon the person and the situation.
His work 'Nicomachean Ethics' is recognised as one of the most influential treatises on morality ever written. It considers in depth what happiness is. When we aim at happiness, we do so for its own sake, not because happiness helps us realize some other end. The goal of the Ethics is to determine how best to achieve happiness.
Happiness
Happiness depends on living in accordance with appropriate virtues. A virtuous person is naturally disposed to behave in the right ways and for the right reasons, and to feel pleasure in behaving rightly. Aristotle describes virtue is a mean state between the extremes of excess and deficiency.
Aristotle maintains that you need friends if you are to achieve a good life. Our feelings for our friends should reflect our feelings for ourselves. He refers to 'self-love', not in the sense that a narcissist loves himself, but in recognition that only people who treat themselves with appropriate care and respect can achieve proper virtue and happiness. Friendship is an important and essential aspect of the good life.
He was also well ahead of Kirkegaard in recognizing the need for an aesthetic dimension to a good life. He believed that pleasure accompanies and perfects our activities. A good person will feel pleasure in doing good things.
It is also essential to fully realize our intellectual virtues through the realization and exercise of our distinctive human mental faculties. Aristotle believed that "Education is the best provision for the journey to old age."
It appears that Aristotle's means of achieving happiness is through a morally just, ethical and virtuous life, brought about through developing good habits and educating the mind to fully realize our intellectual abilities.
Aristotle also had a religious dimension, in fact his influence on religion was considerable. His brand of philosophy influenced the progress of Judaism, Islam and Christianity through thinkers such as Maimonides, Thomas Aquinas and Averroes.
For more information about the great philosophers and their views on narcissism and happiness, read Finding Happiness.