Randy E. Barnett
The problem of interest takes many forms but traces from the common tendency of persons to make judgments or choose actions that they believe will serve their interests. Put another way, people tend to try to satisfy their subjective preferences (although these preferences may not always be self-regarding). Natural rights theorists acknowledged the pervasiveness of this phenomenon by according the impulse towards self-preservation a central place in their theories. As seventeenth-century natural rights theorist, Samuel Pufendorf wrote:
[I]n investigating the condition of man we have assigned the first place to self-love, not because one should under all circumstances prefer only himself before all others or measure everything by his own advantage, distinguishing this from the interests of others, and setting forth as his highest goal, but because man is so framed that he thinks of his own advantage before the welfare of others for the reason that it is his nature to think of his own life before the lives of others.
In an essay on natural law, Pufendorf expanded on his last point:
In common with all living things which have a sense of themselves, man holds nothing more dear than himself, he studies in every way to preserve himself, he strives to acquire what seems good to him and to repel what seems bad to him. The passion is usually so strong that all other passions give way before it. 
The fact that people make choices on the grounds of interest is not, by itself, a problem. Rather, acting out of interest can be considered a problem only against some normative background that distinguishes objectionable from unobjectionable actions. For natural rights theorists, this normative background was supplied by the human need for peaceful social interaction with which self-interested actions can sometimes interfere: Man, then, is an animal with an intense concern for his own preservation, needy by himself, incapable of protection without the help of his fellows, and very well fitted for the mutual provision of benefits. Equally, however, he is at the same time malicious, aggressive, easily provoked and as willing as he is able to inflict harm on others. The conclusion is: in order to be safe, it is necessary for him to be sociable; that is to join forces with men like himself and so conduct himself towards them that they are not given even a plausible excuse for harming him, but rather become willing to preserve and promote his advantages.
Consequently, for Pufendorf: "The laws of this sociality, laws which teach one how to conduct oneself to become a useful member of human society, are called natural laws.
In this Part, I discuss how the liberal conception of justice and the rule of law helps address three distinct problems of interest. In this chapter, I discuss the partiality problem, while the incentive problem is considered in Chapter 8 and the compliance problem in Chapter 9. Handling these additional problems may require that we further refine the conception of justice and the rule of law that was adequate to handle the very different first-, second-, and third-order problems of knowledge.
Nevertheless, the need to handle these problems of interest provides independent support for the liberal conception of justice and the rule of law. Those who urge that these fundamental rights and procedures be abandoned or highly qualified must explain how this vital function can be performed in some other manner. The fact that the discussion of the problems of interest is shorter than the discussion of the knowledge problems reflects, not their relative importance, but the degree to which the problems of interest are far better known and easier to explain than are the problems of knowledge, and the fact that the way the problems of interest are handled by the liberal conception of justice and the rule of law is more widely understood.
 Samuel Pufendorf, De lure Naturae at Gentiun Libri Octo (1672),
trans. C. H. and W. A. Oldfather (New York: Oceana Publications; London:
Wildby and Sons, 1964), Prol. 39. Return