Aristotle's Nicomachean Ethics was written around 340 BC. It is probably named after either his father or son, who were both named Nicomachus. Nicomachean Ethics is Aristotle's most mature work on ethics. That the argument as presented in the book sometimes seems to flow very poorly is due to the fact that the work is actually a series of lectures and was later pieced together (probably by Aristotle's son) and published as a complete work. Still, it is considered to be one of the most accessible of Aristotle's works.
A further difficulty in understanding the work results from the inability to express the full meaning of certain key terms when translating them from Greek into English. The most of these terms are eudamonia and arete, which highly connected. Eudamonia is usually translated as happiness. As understood by the Greeks, eudamonia was not a state but a way of living, and it was inextricably tied to goodness. The Greeks had a teleological view of human life, meaning that there is a natural end toward which human life is directed (telos=end or fulfillment). This end is determined by the function proper to human beings, and consists in performing that function well. Thus the word which we translate as virtue comes from the Greek arete which is the proper excellence or skill of a particular thing. The arete of a knife is to cut well, just as the arete of a human being is to act according to reason.