"Without controversy, it [the word ‘Jehovah’ or ‘Jahweh’] is derived from the word havah…. He is called Jehovah, because He has existence from Himself…. Nor do I agree with th[os]e grammarians who will not have it pronounced…. Because its etymology, of which all confess that God is the Author, is more to me than an hundred rules."
Also Pfeiffer rightly observes in his own Dubia Vexata (on this passage Exodus 6:2): "The name Jehovah was not, strictly and literally, unknown to the fathers" before Moses. "Now every difficulty will be removed, by reading it interrogatively – ‘And by My name Jehovah, was I not known to them?" This rhetorical interrogative presupposes the answer: ‘Of course!’ For "this is both agreeable to the Hebrew idiom and to…the context."