Suppose two changelings want to create a pledge. Changeling A has an open vow slot, but Changeling B has no remaining slots for a vow. Can A make a vow for the pledge while B makes an oath for the same pledge? Or must they either both make vows or both make oaths? If the latter, must they both make the same oath?
All parties involved swear 'on' the same thing - whether it's a Vow, on their name, whatever. They both have to make the same vow, the same oath, swear on the same corporal (or the same type of corporal in the case of, say, two nobles swearing on their titles or two Lost swearing on mortal corporals). The things in a pledge that must be the same are the type of pledge and the duration; tasks, sanctions, and boons may differ between parties so long as the pledge balances out to zero at the end. The exception to this is the Dueling Oath, which you can read more about in Swords at Dawn.