Natural law
Natural law or the law of nature (Latin: lex naturalis) is an ethical theory that posits the existence of a law whose content is set by nature and that therefore has validity everywhere. The phrase natural law is sometimes opposed to the positive law of a given political community, society, or nation-state, and can thus function as a standard by which to criticize that law. In natural law jurisprudence, on the other hand, the content of positive law cannot be known without some reference to the natural law (or something like it); natural law, used in this sense, can be evoked to criticize decisions about the statutes, but less so to criticize the law itself. Natural law can be used synonymously with natural justice or natural right (Latin ius naturale), although most contemporary political and legal theorists separate the two.
Natural law theories have exercised a profound influence on the development of English common law, and have featured greatly in the philosophies of Thomas Aquinas, Francisco Suárez, Thomas Hobbes, Hugo Grotius, Samuel von Pufendorf, and John Locke. Because of the intersection between natural law and natural rights, it has been cited as a component in United States Declaration of Independence.
Against the conventionalism that the distinction between nature and custom could engender, Socrates and his philosophic heirs, Plato and Aristotle, posited the existence of natural justice or natural right (dikaion physikon, Latin ius naturale). Of these, Aristotle is often said to be the father of natural law.
Aristotle's association with natural law is due largely to the interpretation given to his works by Thomas Aquinas.Aquinas's influence was such as to affect a number of early translations of these passages, though more recent translations render them more literally.
The Roman Catholic Church continues to hold the view of natural law set forth by Thomas Aquinas, particularly in his Summa Theologica, and often as filtered through the School of Salamanca. This view is also shared by some Protestant churches.
They understand human beings to consist of body and mind, the physical and the non-physical (or soul perhaps), and that the two are inextricably linked. Humans are capable of discerning the difference between good and evil because they have a conscience. There are many manifestations of the good that we can pursue. Some, like procreation, are common to other animals, while others, like the pursuit of truth, are inclinations peculiar to the capacities of human beings.
To know what is right, one must use one's reason and apply it to Aquinas' precepts. The most important is the primary precept, self preservation. There are also four subsidiary precepts: procreation, education of children, living in society, and worshipping God (veneration). In addition to these, there are secondary precepts, which Aquinas did not specify like the other five. Therefore, for a deontological ethical theory they are open to a surprisingly large amount of interpretation and flexibility. Any rule that helps man to live up to the primary or subsidiary precepts can be a secondary precept, for example:
1. Drunkenness is wrong because it injures one's health, and worse, destroys one's ability to reason, which is fundamental to man as a rational animal (i.e. does not support self preservation).
2. Theft is wrong because it destroys social relations, and man is by nature a social animal (i.e. does not support the subsidiary precept of living in society).
Natural moral law is concerned with both exterior and interior acts, also know as action and motive. Simply doing the right thing is not enough; to be truly moral one's motive must be right as well. For example, helping an old lady across the road (good exterior act) to impress someone (bad interior act) is wrong. However, good intentions don’t always lead to good actions. The motive must coincide with Aquinas's cardinal or theological virtues.
Source : http://en.wikipedia.org