Even those who believe in [modern] tongues acknowledge that unsaved people have tongues experiences. There is nothing supernatural about them. But there is something unique about speaking complete and meaningful sentences and discourses in a knowable language to which one has never been exposed. This is what the real New Testament gift of tongues entailed. Anything short of this, as “private tongues” are, should not be considered the biblical gift of tongues.
Norman Geisler