The most general duties in natural law, Crusius begins, are those that we are obligated to perform to everyone, no matter what the particular stand in life is and no matter what further contracts or agreements we might have made with them. In other words, they are the duties that we should be able to deduce without any further assumptions from the basic principle of natural law.
One of these duties (or more likely, a combination of several related duties) is that we should always be joyfully ready to serve and help a person in need of assistance - for instance, if we find a lost tourist in our hometown, we should be ready to show where she has to go. This is a general duty, Crusius affirms, that we are obligated to perform to anyone, no matter who they are. Even our enemies do not make an exception, and furthermore, we shouldn’t even hate or envy them. Still, this does not mean we are not allowed to make any preferences, Crusius accedes, since we are more obligated to serve friends, as long as we do it fairly and equitably.
Crusius doesn’t think that we are obligated to serve people without any reward, but admits that usually services are to be paid for in some form. It is only when people do not have the means to pay that we might be obligated to help them without reward, and even this obligation is not so strict if the people in question can help themselves, if they are to blame for their condition or if someone else could help them. Furthermore, even if no other reward for a service can be expected, the one assisted is obligated to be thankful for help. Analogically to a demand for a reward, if someone offends us, we have a right to expect the offender to repay the deed.
Furthermore, Crusius continues, if circumstances permit it, we should try to be truthful, that is, what we think should correspond to what our words mean. Here the conditional is important, and Crusius is not willing to go down the route where Kant - at least as he is usually interpreted - would go. That is, Crusius does not want to say that we are always obligated to speak truth, because in some cases this might break some other duties. He still advises to avoid straight out lies, even if they were made with good intentions. Instead, Crusius allows dissemblance, for instance, using silence and gestures to suggest that things are otherwise than they actually are.
In addition to the duties aimed strictly toward other people, Crusius notes that dealings with other people create an obligation to do something for ourselves. That is, in order to serve others we have to have abilities by which we can help them, which means that we are obligated to cultivate our skills. Partially, Crusius reminds us, this duty of self-cultivation has already been dealt with in ethics, but there are still certain aspects of this cultivation that concern the natural law more. A particular example is the need for what Crusius calls decorum, in other words, what is considered to be external signs of virtue - say, one has to dress in a manner that a decent person is expected to dress in one’s own society. Although decorum is not virtue as such, it at least implies to the onlooker that she is seeing a virtuous person, Crusius suggests - or at least it doesn’t deter her. Thus, decorum is of assistance in making people want to ask help from you.
Crusius also notes that if a society is to work properly, all people cannot cultivate the same abilities, even if they were abilities required for the noblest causes. Thus, a need for particular life careers arises. Crusius considers the possibility that each person would pursue the career that is best suited to a person. Yet, he remarks, it is too difficult to determine what would be the best career for each person. Instead, Crusius advises everyone to strive for a career, which suits their wishes and doesn’t waste their talents - or even earlier, their parents should find out what the person likes and guide them toward it. This strategy works, Crusius thinks, because person’s desires usually show what they are most suited to do - desire for a certain career should come out naturally, and as all things natural are God’s design, this desire must be good.
