Natural law theory is not a single theory of law, but the application of ethical or political theories to the questions of how legal orders can acquire, or have legitimacy, and is often presented as a history of such ethical and political ideas.
These theories would explained the nature of morality, thus making natural law theory a general moral theory. The basic idea was that man could come to understand, either by his own reasoning or help from God, how he should act rightly in respect of his fellow man. However, within modern jurisprudence, much of the importance of natural law has been eroded from a question on the meaning of justice or how a system of law could be understood as legitimate; into a question of what is the relationship between natural law theories and the everyday operations of a legal system.
This is because much of natural law has been savaged by two criticisms: a. Natural law theories' assertion that in order to understand what law is, it is necessary to involve oneself in an exploration and explaination of what law ought to be is inherrently faulty. (the fact/value distinction)
This confuses the description (law's actual existence) with prescription (the evaluation of law as good or bad). Natural law theories stray between the logically unconnect fields of meaning of 'is' and 'ought', which is dubbed the 'naturalistic fallacy'.
The incompatibility between these two fields is illustrated by the classic interpretation of Hume's law, that one cannot derive a statement about what ought to be from a statement about what is, or vice versa. To give an example of the non sequitur involved in this kind of reasoning is that the fact that only women can bear children, points to the conclusion that they This supposed link between the capacity to bear children and motherhood is provided through social conventions and is entirely contingent. The former does not follow the latter as if it was some...