"And the king was sorry: nevertheless for the oath's sake, and them which sat with him at meat, he commanded it to be given her." (Matthew 14:9, KJV)
The word translated as the singular "oath's" in the KJV is the plural noun, "ορκους". The KJV appears to treat the plural ορκους as a categorical plural and renders the English word in the singular. Greek scholar Daniel Wallace says with respect to the categorical plural, "The reason that the plural is used is that it more easily yields itself to a generic notion: The force of this usage, it seems, is to focus more on the action than on the actor" (Greek Grammar Beyond the Basics, p. 404). Wallace continues his explanation by providing examples where it is appropriate to render a Greek plural in the singular when the context suggests a singular. When we see the context of Matthew 14:9, there was only one specific oath given by Herod. Just two verses back at Matthew 14:7, we read that Herod promised with an oath (ορκου, singular). In such a case, it is acceptable to treat "ορκους" as a plural only in the generic sense. It is helpful to translate it in the singular for the English audience that would otherwise see a contradiction between the singular oath in verse 7 and the plural oaths in verse 9 (a Koine Greek audience would not have regarded this as a contradiction). This is not to say that "ορκους" absolutely has to be translated as a singular, but a translator is entitled to make that choice. The KJV does not always translate categorical plurals as singulars because whether or not to do so is discretionary.
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