IV. Second, they falsely argue from the ignorance of a thing to its negation, as if it was necessary for a thing not to be because it is not known. And yet the truth of the thing is to be measured from itself, not from our knowledge or ignorance. For who doubts that other thing is able to be which is concealed from me and others, whether because it is a secret and hidden or because we do not diligently attended to the investigation of it? This inference formerly beclouded Elijah, who, since he did not know where the church of his time was, nor who were its teachers, thought he was alone because the others were unknown to him (1K10:10; Rom 11:4). But the Lord taught him that this reasoning was faulty when he said, “yes I have left me 7000 in Israel, all the knees which have not bowed unto Baal” (1K. 19:18). If therefore the Israelite church could thus lie concealed so that Elijah was ignorant of it, who will wonder that same thing happened in the time of our ancestors?
V. Third, they also reason faultily from the ignorance of place to the negation of the thing. For although the place of a thing may be unknown to me it does not follow that the thing itself does not exist absolutely. Although I may not know where treasures in the sea, it must not on that account be denied that they are there. Thus it is one thing to know that there is a true church; another to know where it is. Of the first, I may be persuaded, although I may know nothing certainly about the second.
Francis Turretin, Institutes of Elenctic Theology 18.10.4–5.