Natural Law and Other Kinds of Law

Grotius gives the following definition of natural law:

The law of nature is a dictate of right reason, which points out that an act, according as it is or is not in conformity with rational nature, has in it a quality of moral baseness or moral necessity; and that, in consequence, such an act is either forbidden or enjoined by the author of nature, God.

IBP, I.1.10.1^{[675] [676] [677] [678]}

To understand this definition, we must take into consideration what Grotius stated in the preceding part of his exposition. In particular, he stated that law (jus) can be synonymous with statute (lex) if what we mean is â€?a rule (regula) of moral actions imposing obligation to [do] what is right' (iBP, 1.1.9.1).2¹ Statutes are by their nature binding, which distinguishes them from mere counsels and instructions.22 Obligation imposed on us by law is to act in a moral fashion. In proposing this approach to law, Grotius follows Aristotle, who claimed that the purpose of law is to ordain what is good?³ Natural law is then a rule which binds people to acting in a way that conforms to their rational nature. Grotius describes this rule further as a â€?dictate of right reason', which indicates that actions which are in conformity with the rational nature contain an element of moral necessity, while those which contradict our natural nature have an element of baseness, moral depravity. According to Grotius, his concept of right reason implies that behavior is ethical if it maintains the natural order (ordo naturalis) and is in agreement with the order of reason (natura rationalis).^[679] And he explicitly adds that it is only as a consequence of the dictate of right reason that an act that is compatible or incompatible with the rational human nature is either commanded (praecipi) or forbidden by the â€?Author of nature,' that is, by God.

The difference between the natural law and volitional divine law is then explained as follows: �volitional divine law does not enjoin or forbid those things which in themselves and by their own nature are obligatory or not per­missible, but by forbidding things it makes them unlawful, and by command­ing things it makes them obligatory' (ibp, 1.1.10.2).

The source of the obligation is different in the two kinds of law, so that while in natural law, the source of obligation rests in the nature of things themselves, in volitional divine law, the obligation is derived from God's will.^[680] On top of that, the natural law applies not only to things outside the sphere of human will but also to many things which are the result of an act of human will. Grotius illustrates this on the example of ownership (dominium), saying that �owner­ship, such as now obtains, was introduced by the will of man; but, once intro­duced, the law of nature points out (indicat) that it is wrong for me, against your will, to take away that which is subject to your ownership' (ibp, 1.1.10.4).

According to Grotius, an important characteristic of the natural law is that it is immutable, even in the sense that it cannot be changed by God. This is because

[m]easureless as is the power of God, nevertheless it can be said that there are certain things over which that power does not extend; for things of which this is said are spoken only, having no sense corresponding with reality and being mutually contradictory. Just as even God, then, cannot cause that two times two should not make four, so He cannot cause that which is intrinsically evil be not evil.

IBP, I.1.10.5

In this passage, Grotius notes that while God as the creator and author of life, imbued things with their natures, this nature now belongs to them inherently and even God's will cannot change it.^{[681] [682] For instance, the laws of mathematics have such a nature, and the situation is similar for natural law in moral philos­ophy. Both areas, meanwhile, are an expression of human rational nature?7}

Grotius tries to demonstrate the existence of natural law in two ways:

Proof a priori consists in demonstrating the necessary agreement or disa­greement of anything with a rational and social nature; proof a posteriori in concluding, if not with absolute assurance, at least with every proba­bility, that that is according to the law of nature which is believed to be such among all nations, or among all those that are more advanced in civilization. For an effect that is universal demands a universal cause; and the cause of such an opinion can hardly be anything else than the feeling which is called the common sense (sensum communis) of mankind.

IBP, 1.1.12.1

A stricter a priori argument is based on showing that some behaviors (rei ali­cuius) are in agreement with human rational and social nature, that human nature demands it.^[683] Such behaviours then become a precept of natural law, for instance the keeping of mutual agreements. A looser a posteriori argument, on the other hand, consists of a generalization of some behaviour about which all people or at least all civilized nations agree that it can be considered part of the natural law. This may pertain to things such as banning sexual intercourse between parents and children. Grotius believes that some behaviors can be generalized because all people share some common sense (sensus communis). Every person has some notion of what is compatible with human social and rational nature, and this commonplace awareness can be viewed as the com­mon sense.

Let us now have a look at how Grotius uses the natural law as a basis of the law of nations. He criticizes the distinction between the two as the Romans conceived of it:

The distinction, which appears in the books of Roman law, between an unchangeable law common to animals and man, which the Roman legal writers call the law of nature in a more restricted sense, and a law pecu­liar to man, which they frequently call the law of nations, is of hardly any value. For, strictly speaking, only a being that applies general principles is capable of law.

IBP, 1.1.11.1

Already in the Prolegomena Grotius showed that one can only speak of nat­ural law among humans, i.e., not among animals. When formulating the law of nations, Grotius takes as his starting point his definition of law as a moral rule or statute. Within thus defined law he then distinguishes between natural law and established or volitional law (ius voluntarium) (ibp, 1.1.9.2). Volitional law originates in the will and can be either human or divine (ibp, i.i.8), whereas human law can be further divided according to its sphere in municipal law (ius civile) and the law of nations (ius gentium). Municipal law is derived from civil power (potestate civili) and Grotius does not treat it further. The law of nations has a wider application because it �is the law which has received its obligatory force from the will of all nations, or of many nations' (ibp, 1.14.1).

The source of obligatoriness of the law of nations is in their will, that is, in the will expressed in agreements they conclude among themselves. With reference to its extent, Grotius notes that �outside of the sphere of the law of nature, which is also frequently called the law of nations, there is hardly any law common to all nations'. One can prove that such law exists by pointing out that it can be found �in unbroken custom and the testimony of those who are skilled in it' (ibp, 1.1.14.2) and it can best be studied by analyzing examples given by �the illustrious writers of history.' According to Grotius - and contrary to Suarez (dl, 11.20.2) - the law of nations thus is not derived from natural law.

The other kind of volitional law is divine law. Grotius distinguishes between a universal divine law and divine law peculiar to a single people. The former is law that was given to humankind by God three times: �[I]mmediately after the creation of man, a second time in the renewal of human kind after the Flood, lastly in the more exalted renewal through Christ' (ibp, 1.1.15.2). These three elements are, according to Grotius, binding to all people inasmuch they are known to them. The Hebrew law, on the other hand, is binding only to Jews, since �the binding force of [the Hebraic] law comes from the will of him who makes the law; and it is not possible to discover, from any indica­tion, that God willed that others than Israelites should be bound by that law' (ibp, I.1.16.7).

Grotius then uses all these three kinds of law to outline a system of laws in the second and third book of his treatise, whereby natural law and the law of nations occupy within the system an especially prominent role. Let us now look at how Grotius uses all these three kinds of law in a particular case, namely, to justify a �just war'.

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