HKB
head, or by his son, or by some other thing that he loves, even as the Apostle swore (2 Cor. 1:23), saying: "I call God to witness upon my soul."
As to Joseph's oath by the health of Pharaoh this may be understood in both ways: either by way of a curse, as though he pledged Pharao's health to God; or by way of contestation, as though he appealed to the truth of God's justice which the princes of the earth are appointed to execute.
Reply Obj. 1: Our Lord forbade us to swear by creatures so as to give them the reverence due to God. Hence Jerome adds that "the Jews, through swearing by the angels and the like, worshipped creatures with a Divine honor."
In the same sense a cleric is punished, according to the canons (22, qu. i, can. Clericum, Obj. 2), for swearing by a creature, for this savors of the blasphemy of unbelief. Hence in the next chapter, it is said: "If any one swears by God's hair or head, or otherwise utter blasphemy against God, and he be in ecclesiastical orders, let him be degraded."
This suffices for the Reply to the Second Objection.
Reply Obj. 3: Religious worship is shown to one whose testimony is invoked by oath: hence the prohibition (Ex. 23:13): "By the name of strange gods you shall not swear." But religious worship is not given to creatures employed in an oath in the ways mentioned above.
SEVENTH ARTICLE [II-II, Q. 89, Art. 7]
Whether an Oath Has a Binding Force?
Objection 1: It would seem that an oath has no binding force. An oath is employed in order to confirm the truth of an assertion. But when a person makes an assertion about the future his assertion is true, though it may not be verified. Thus Paul lied not (2 Cor. 1:15, seqq.) though he went not to Corinth, as he had said he would (1 Cor. 16:5). Therefore it seems that an oath is not binding.
Obj. 2: Further, virtue is not contrary to virtue (Categ. viii, 22). Now an oath is an act of virtue, as stated above (A. 4). But it would sometimes be contrary to virtue, or an obstacle thereto, if one were to fulfil what one has sworn to do: for instance, if one were to swear to commit a sin, or to desist from some virtuous action. Therefore an oath is not always binding.
Obj. 3: Further, sometimes a man is compelled against his will to promise something under oath. Now, "such a person is loosed by the Roman Pontiffs from the bond of his oath" (Extra, De Jurejur., cap. Verum in ea quaest., etc.). Therefore an oath is not always binding.
Obj. 4: Further, no person can be under two opposite obligations. Yet sometimes the person who swears and the person to whom he swears have opposite intentions. Therefore an oath cannot always be binding.
On the contrary, It is written (Matt. 5:33): "Thou shalt perform thy oaths to the Lord."
I answer that, An obligation implies something to be done or omitted; so that apparently it regards neither the declaratory oath (which is about something present or past), nor such oaths as are about something to be effected by some other cause (as, for example, if one were to swear that it would rain tomorrow), but only such as are about things to be done by the person who swears.