The question on the relationship between legal validity and morality is a perennial one. There are the legal positivists who tend to rally around Austin’s claim that “the existence of law is one thing; it’s merit or demerit is another” and there are the natural lawyers who tend to follow Augustine’s claim that “a law which is unjust seems to be no law at all”  .  Amidst the struggle in reaching a definitive resolution on this question, the work of Professor H.L.A Hart has made significant contributions to this area of contention from a “soft”  positivist perspective. Not only does Hart claim that “it is in no sense a necessary truth that laws reproduce or satisfy certain demands of morality”  , but he explicitly acknowledges that “the rule of recognition may incorporate as criteria of legal validity conformity with moral principles or substantive values”  . He also goes a step further and makes a concession that there is a “core of good sense in the doctrine of Natural Law”  .
In The Concept of Law, Hart expounds on what he takes to be “the minimum content of natural law”  . His minimum content of natural law rests upon, “the generalaˆ¦argumentaˆ¦that without such a content laws and morals could not forward the minimum purpose of survival which men have in associating with each other.” 
Hart argues that there are five features of human condition which sometimes work against survival and believes that every legal system must take these into account. As such, Hart, who claims to be a legal positivist, acknowledges that there is a connection between law and human nature based on the following truisms  ;
Human vulnerability, which dictates the proscription of violence. The argument lies in the simple fact that “men are both occasionally prone to, and normally vulnerable to, bodily attack”  . Thus, if there are no such rules restricting violence, there would be no point in having rules of any other kind  .
Approximate equality, meaning that although men have different capacities, no individual is “so much more powerful than others, that he is able, without co-operation, to dominate or subdue them for more than a short period of time”  . Thus, there is a need for a “system of mutual forbearance and compromise which is the base of both legal and moral obligation”  .
Limited altruism, which makes rules of mutual forbearance necessary to secure a balance between altruistic and selfish inclinations in a social pattern of life  .
Limited resources, meaning that since necessities needed by men for survival are limited and can only, be won though labour, there is a need for a “minimal form of the institution of propertyaˆ¦and the distinctive kind of rule which requires respect for it”  .
Limited understanding and strength of will, which tempt individuals into deviant or anti-social conduct for short-term personal gain thus, rendering sanctions as crucial to ensure compliance with the rules. 
As such, Hart argues that there is a natural necessity that legal systems contain rules for the “protection of persons, property and promises”  . These are the rules of conduct which any social organisation must contain if it is to be viable and which are necessitated by certain contingent truisms about human beings and the world in which they live.  Therefore, taking the premise to be that all human beings desire to live or survive, it is concluded that every legal system has for that very reason these universally accepted principles which form the minimum content of natural law, and which are common to law and morality.
It submitted that Hart’s minimum content of natural law is indeed thoroughly minimal. In advancing his minimum content of natural law, Hart “simply offers a very humean set of assertions, of them made as empirical generalisations, not a priori truths, about limited altruism, vulnerability, approximate equality and limited resources”  . It is also rather restricted to rules relating to injury, property, life and death. This is due to the fact that Hart has only taken into account the sole basic aim of survival. As a result, those moral rules that do not concern the aim of survival will not be included. In addition, there is also some truth to Hart’s empirical generalisations concerning human nature. Human beings are generally vulnerable and the strongest individual is capable of being killed by a group of weaker individuals as men “are not giant crabs, with impenetrable shells”  . Furthermore, there is a real problem of resources being scarce, thus our wants tend to outstrip what is available to supply them  . As such, enforceable rules are required to overcome the problems posed and this is something which every legal system should take into account.
Therefore, it is very difficult to dissent from Hart’s minimum content of morality which comprises of those necessary norms of social interaction which while reflecting moral considerations, are necessary for any system of law to be minimally effective as a legal system. In fact, in most legal systems, fundamental moral norms are enshrined in law as basic criminal prohibitions. Rules forbidding murder is one example and such a rule is indeed crucial for a society to be viable. Many such provisions seem to reaffirm the moral base of social order and penalise those who do not follow the rules.
However, it is debatable as to whether survival is the sole aim that can be generally predicated of man and his societies. Generally, the aim of man is to not only survive, but to survive well, and to live according to some conceptions of a desirable, good or just life. As such, laws in a social organisation would need to embody men’s needs to survive as well as their conceptions of what is desirable, good and just. Therefore, Patterson suggests that “any definition of the ultimate end of man should therefore take into account not only the biological facet of man’s existence but also man’s unique intellectual and social capacities”  . This point is made by Rolf Sartorius who asserted that “Hart’s notion of natural necessity is presented in terms of what there are good reasons for given survival as an aim. But surely room must be made for loftier human pursuits than mere survival (of either the individual or species). I suspect that some attempt at realizing those social and environmental conditions which provide an opportunity for individuals to lead meaningful lives will have to be made here.” 
Hart justifies his refusal to take into account a man’s unique intellectual and social capacities on the premise that there are too many definition and that there is a lack of consensus over which is correct  . It has been argued by Patterson, that Hart places too much focus on aspects of classical natural law theory that he fails to consider the Finnis’s account of man’s ultimate end  . His account states that “no determinate one natural last end or determinate unifying principles of individual or social life”  but that man’s ultimate end is “the participation by a multiplicity of persons in a manifold of goods”  . These goods exclude “no aspect of individual wellbeing and is potentially affected by every aspect of every life plan”  . Thus, Patterson concludes that because “they include life in addition to a plurality of other goods such as knowledge, friendship, religion and play, all of which account not only for the biological aspects of man but also the rational and social, it negates the need for Hart’s cautiousness in having to select one ultimate principle or good”  . Thus, it is submitted that the survival, being defined as the ultimate end of man is too simplistic and does not truly reflect the true situation.
Furthermore, it is also argued that there is a need for procedural requirements within the law to ensure the survival of all the members of the society and that it is not sufficient to only merely comply with Hart’s minimal moral content  . Hart suggests that for a society to be viable, it “must offer some of its members a system of mutual forbearances, but, it need not, unfortunately, offer them to all”  . Hart proposes this despite admitting to the possibility that in extreme circumstances when a sufficiently large number of people are oppressed and derived of protection from the law, the legal system may become “unstable with latent treat of upheaval”  and may eventually collapse.
Although Hart, in his later article, recognises that “all men who have aims to pursue need the various protections and benefits which only laws conforming to … requirements of substance and procedure can effectively confer”  and that “laws, however, impeccable their content, may be of little service to human beings and may cause both injustice and misery unless they generally conform to certain requirements which may broadly be termed procedural”  , he does not include any such procedural requirement into the minimum moral content of law. Accordingly, despite highlighting the “importance of the rule of law as embodied in certain requirements of procedural fairness, Hart fails to explicitly broaden the minimum moral content of law so as to include them”  .
Consequently, Patterson suggests that the requirement of fairness and justice must be taken into account in order to ensure the survival of the members of a particular society as well as the legal system  . This suggestion is further supported by Hart’s later acknowledgement that the purpose of law does not only ensure survival but facilitates the pursuit of aims as well  . The reason for Hart failing to take into account requirements of fairness or justice within his minimum moral content of law could be due to his claim that it is possible for a legal system to exist even though much of its substantive and procedural content is unfair or immoral. However, “beyond a certain point, a system sufficiently lacking in fairness or justice can collapse even though it conforms to Hart’s minimum moral content because, according to Hart, the more a system is oppressive and unjust, the more likely it will be unstable”  .
In conclusion, Hart correctly concedes to that fact that there needs to be a minimum moral content in law to ensure the survival of the members of the society. However, it is argued that mere adherence to Hart’s minimum content of moral itself will not ensure the survival of the members in a society. Procedural fairness should be incorporated within the law in order to ensure survival of the members of the society and the stability and continuance of the legal system.