Upon hearing a radio announcement that a celebrated high school football player had made a verbal commitment to play for a certain college team, I was left wondering what alternative form of communication the boy might have employed for this purpose—an upward-pointing thumb gestured in the direction of his new coach, perhaps?
Garner classifies this usage—the substitution of verbal for oral—as a "slipshod extension", Fowler's term for the stretching of a word beyond its true meaning, a phenomenon that is "especially likely to occur when some accident gives currency among the uneducated to words of learned origin ...."* However, the extended meaning in this case is generally supported by contemporary dictionaries, and was already observed by the editors of Webster's 2nd in their definition of verbal:
2. Expressed in words, whether spoken or written, but commonly in spoken words; hence, by confusion, spoken; ....Furthermore, lest we attempt to dismiss this confusion as a recent development, it should be noted that as early as 1756, Dr. Johnson listed "Spoken, not written" as the primary meaning of the word. In light of all this documentary evidence, it would appear that the best we can do is to recommend the use of oral in place of verbal when that meaning is intended, on grounds of precision.
On the other hand, it must further be conceded that since verbal communication is not the only function of the mouth, oral is itself occasionally prone to ambiguity, as in the sentence She expressed her gratitude orally.