They argued that a rightful government can impose moral obligations on actions that are otherwise morally neutral by forbidding or requiring them. However, this power does not extend to intrinsically just or unjust actions.
Natural law consists of precepts that are inherent to human nature and cannot be changed by any human authority. Human law, on the other hand, builds on natural law and can impose additional obligations, but must remain consistent with natural law.
For thinkers like Vitoria, natural law and human reason are essentially the same, as the precepts of natural law are the conclusions of practical reasoning. Others, like Suarez, argued that divine commands are necessary to create obligations, even though the natural badness of actions like murder is known through reason.
The law of nations was seen as a set of rules arising from a tacit agreement among all peoples to follow certain norms, allowing for peaceful coexistence. It was based on natural law but added specific obligations, such as property rights and the regulation of relationships between states.
Molina argued that slavery was introduced by the law of nations, even though all humans are naturally free. It was justified in cases of just war or when individuals voluntarily enslaved themselves as a last resort for survival.
While some, like Tomas de Mercado, supported government intervention in pricing to benefit society, others, like Molina, believed that prices should reflect the natural price determined by market forces. Molina argued that government interference often favored the wealthy over the poor.
They sought a middle ground, allowing for the charging of interest to cover the costs and risks of lending, but not for excessive profit. The correct amount of interest was determined by the lender's actual costs and missed opportunities, similar to how the just price of goods was determined.
They recognized that money could be a form of capital, capable of generating value through investment. However, they emphasized that lenders should only be fairly compensated for their risks and missed opportunities, rather than seeking profit.
Vitoria, Molina, Suárez and others develop the idea of natural law, exploring its relevance for topics including international law, slavery, and the ethics of economic exchange.