Article I: On the Directive Force or Obligation of Law

233. The proper effect of law is obligation. This holds a middle place among the various effects of law: its ultimate effect on the part of the legislator is obligation actively regarded, or the power of binding which resides in the law; to this there corresponds in subjects, as the first effect, obligation passively regarded, that is, the moral bond itself and the necessity of obeying.

But obligation is a moral necessity of doing or omitting something, categorical or imperative. It is called:

1. a moral or objective necessity, which befits a free being and by which something is necessary by the necessity of the end (as means or precept), so that without it the end is not obtained. Whence it is a moral bond or practical necessity of choosing means to the end, by which, on the supposition of the end, such a means must necessarily be furnished; and thus it is distinguished from a physical bond or the physical subjective necessity of efficiency, both natural, which takes away liberty, and of coercion, which also destroys the voluntary;

2. categorical or imperative, that is, not only conditional, on the supposition of the end if someone wishes to obtain it, but absolute, by which the end itself is imposed. Whence obligation arises from a twofold necessity: from the absolute necessity of the act with respect to the ultimate end, and from the absolute necessity of this end. And thus it is made manifest how it does not harm liberty: it binds the will insofar as the intellect proposes the end and the means, while leaving untouched the physical power of acting or not acting.

1. Cf. Q. D. De Veritate 17, a. 3; I, q. 87, a. 1; I-II, q. 99, a. 1; II-II, q. 44, a. 1; q. 55, a. 3, ad 2; Contra Gentiles I, 67; II, 29; Quodlibet V, 19.

In other words, obligation imports a twofold debt: one according to itself, and thus the end is due; the other on account of another thing, that is, without which it is impossible to arrive at the end. And thus "in debt there is an order of exigency or necessity of something to that to which it is ordered" (I, q. 21, a. 1, ad 3).

Hence obligation, like morality, is an intrinsic habitude and real order, or transcendental relation:

a) in the obligatory act, just as morality is the real order of conformity or difformity, so obligation is the real order of necessity to the object and ultimate end (I-II, q. 99, a. 1);

b) in the obligated person, it is not only a relation of subjection to the person of the legislator, which is presupposed, but adds a new relation by which he is subjected as to this or that prescription (II-II, q. 16, a. 1).

Obligation, therefore, is a property of a human act according to which it is said to be necessarily placed or avoided for the ultimate end.

234. Division of law by reason of diverse obligation. - Obligation is diverse according as law has directive force or coercive force, and therefore by reason of effect or diverse obligation, one law is moral or preceptive, which only directs and obligates to placing or omitting an act; another is penal, which only punishes him who has omitted the prescribed act or placed the prohibited act; another is mixed, which does both. Every law obligates in conscience to something which the legislator intends; otherwise it would not be a true law but a counsel. But this is the difference between a purely preceptive law and a purely penal law: the first only obligates to placing or omitting the act established by law, without inflicting a penalty upon transgressors, namely: let everyone do this, for example, hear Mass; the second obligates only to undergoing the penalty which the law exacts from him who has not placed or has omitted the established act, namely: he who has done this, for example, who before this day has hunted or fished, is to pay money. For since in positive law the whole obligation depends upon the legislator, just as he can not obligate, so he can obligate more or less, or to the penalty alone. From these is distinguished mixed law, which is preceptive or moral and also penal, namely, let no one do this under penalty: this obligates in conscience to placing or omitting the act and at the same time to undergoing the penalty if it has not been placed or omitted; but the merely penal law does not obligate in conscience to placing the act, but under the penalty alone, to which nevertheless it binds in conscience.

1. There is not one mode in which they conceive merely penal law. Some say that moral and at the same time penal law, or mixed law, obligates conjunctively to two things: both to doing the prescribed work and at the same time to undergoing the penalty if it has not been done; but merely penal law disjunctively: either to placing the work, or to undergoing the penalty if it has not been placed. Thus Laymann, the Salmanticenses, d'Annibale, Bouquillon, Haine, Marc, and Tanquerey seem to speak. On the contrary, others assert that mixed law obligates to two things: to one absolutely, namely, to placing the prescribed work; but to the other conditionally, namely, to the penalty, if the work has not been placed; while merely penal law obligates only to one thing conditionally and hypothetically, namely, to paying the penalty, if the work intended by the legislator has not been fulfilled. For the legislator thinks and intends that his scope can be obtained by the mere threat and obligation of penalty. But if it is objected that penalty supposes fault, they respond that it does not necessarily suppose fault in the forum of conscience, but juridical fault in the external forum and before human law suffices: a transgression of the order constituted by law. Thus Suarez, Billuart, Noldin, Koch, Wernz, Prummer, Maroto, Vermeersch, and A. Janssen are said to hold. That St. Thomas admitted merely penal laws is clear from II-II, q. 186, a. 9, ad 1.

By reason of form, moral law is distinguished into affirmative or commanding law, which imposes something to be done, and negative or prohibiting law, which imposes something to be omitted; the former obligates always but not for always, that is, only for some time during which it endures; the latter obligates always and for always, that is, for every time during which it endures. And indeed at any time we are bound to abstain from every evil, but not to do every good.

1. Affirmative and negative are to be taken not from the words but from the end.

To preceptive law is reduced the law which, permitting, commands the liberty of someone and prohibits that it be impeded by others; to penal law rather is reduced the law which, invalidating, coerces by invalidating an act placed against the law.