Objection 1. It seems that obedience is not a special virtue. For disobedience is contrary to obedience. But disobedience is a general sin, because Ambrose says (De Parad. viii) that "sin is to disobey the divine law." Therefore obedience is not a special virtue.
Objection 2. Further, every special virtue is either theological or moral. But obedience is not a theological virtue, since it is not comprised under faith, hope or charity. Nor is it a moral virtue, since it does not hold the mean between excess and deficiency, for the more obedient one is the more is one praised. Therefore obedience is not a special virtue.
Objection 3. Further, Gregory says (Moral. xxxv) that "obedience is the more meritorious and praiseworthy, the less it holds its own." But every special virtue is the more to be praised the more it holds its own, since virtue requires a man to exercise his will and choice, as stated in Ethic. ii, 4. Therefore obedience is not a special virtue.
Objection 4. Further, virtues differ in species according to their objects. Now the object of obedience would seem to be the command of a superior, of which, apparently, there are as many kinds as there are degrees of superiority. Therefore obedience is a general virtue, comprising many special virtues.
On the contrary, obedience is reckoned by some to be a part of justice, as stated above (Article 80).
I answer that, A special virtue is assigned to all good deeds that have a special reason of praise: for it belongs properly to virtue to render a deed good. Now obedience to a superior is due in accordance with the divinely established order of things, as shown above (Article 1), and therefore it is a good, since good consists in mode, species and order, as Augustine states (De Natura Boni iii) [Cf. I, 5, 5]. Again, this act has a special aspect of praiseworthiness by reason of its object. For while subjects have many obligations towards their superiors, this one, that they are bound to obey their commands, stands out as special among the rest. Wherefore obedience is a special virtue, and its specific object is a command tacit or express, because the superior's will, however it become known, is a tacit precept, and a man's obedience seems to be all the more prompt, forasmuch as by obeying he forestalls the express command as soon as he understands his superior's will.
Reply to Objection 1. Nothing prevents the one same material object from admitting two special aspects to which two special virtues correspond: thus a soldier, by defending his king's fortress, fulfils both an act of fortitude, by facing the danger of death for a good end, and an act of justice, by rendering due service to his lord. Accordingly the aspect of precept, which obedience considers, occurs in acts of all virtues, but not in all acts of virtue, since not all acts of virtue are a matter of precept, as stated above (I-II, 96, 3). Moreover, certain things are sometimes a matter of precept, and pertain to no other virtue, such things for instance as are not evil except because they are forbidden. Wherefore, if obedience be taken in its proper sense, as considering formally and intentionally the aspect of precept, it will be a special virtue, and disobedience a special sin: because in this way it is requisite for obedience that one perform an act of justice or of some other virtue with the intention of fulfilling a precept; and for disobedience that one treat the precept with actual contempt. On the other hand, if obedience be taken in a wide sense for the performance of any action that may be a matter of precept, and disobedience for the omission of that action through any intention whatever, then obedience will be a general virtue, and disobedience a general sin.
Reply to Objection 2. Obedience is not a theological virtue, for its direct object is not God, but the precept of any superior, whether expressed or inferred, namely, a simple word of the superior, indicating his will, and which the obedient subject obeys promptly, according to Titus 3:1, "Admonish them to be subject to princes, and to obey at a word," etc.
It is, however, a moral virtue, since it is a part of justice, and it observes the mean between excess and deficiency. Excess thereof is measured in respect, not of quantity, but of other circumstances, in so far as a man obeys either whom he ought not, or in matters wherein he ought not to obey, as we have stated above regarding religion (92, 2). We may also reply that as in justice, excess is in the person who retains another's property, and deficiency in the person who does not receive his due, according to the Philosopher (Ethic. v, 4), so too obedience observes the mean between excess on the part of him who fails to pay due obedience to his superior, since he exceeds in fulfilling his own will, and deficiency on the part of the superior, who does not receive obedience. Wherefore in this way obedience will be a mean between two forms of wickedness, as was stated above concerning justice (58, 10).
Reply to Objection 3. Obedience, like every virtue requires the will to be prompt towards its proper object, but not towards that which is repugnant to it. Now the proper object of obedience is a precept, and this proceeds from another's will. Wherefore obedience make a man's will prompt in fulfilling the will of another, the maker, namely, of the precept. If that which is prescribed to him is willed by him for its own sake apart from its being prescribed, as happens in agreeable matters, he tends towards it at once by his own will and seems to comply, not on account of the precept, but on account of his own will. But if that which is prescribed is nowise willed for its own sake, but, considered in itself, repugnant to his own will, as happens in disagreeable matters, then it is quite evident that it is not fulfilled except on account of the precept. Hence Gregory says (Moral. xxxv) that "obedience perishes or diminishes when it holds its own in agreeable matters," because, to wit, one's own will seems to tend principally, not to the accomplishment of the precept, but to the fulfilment of one's own desire; but that "it increases in disagreeable or difficult matters," because there one's own will tends to nothing beside the precept. Yet this must be understood as regards outward appearances: for, on the other hand, according to the judgment of God, Who searches the heart, it may happen that even in agreeable matters obedience, while holding its own, is nonetheless praiseworthy, provided the will of him that obeys tend no less devotedly [Cf. 82, 2] to the fulfilment of the precept.
Reply to Objection 4. Reverence regards directly the person that excels: wherefore it admits a various species according to the various aspects of excellence. Obedience, on the other hand, regards the precept of the person that excels, and therefore admits of only one aspect. And since obedience is due to a person's precept on account of reverence to him, it follows that obedience to a man is of one species, though the causes from which it proceeds differ specifically.
Source: Summa Theologica (New Advent)