Many men have their master's degree but do not know the master. And they were all filled with the Holy Ghost, and began to speak with other tongues, as the Spirit gave them utterance. For they heard them speak with tongues, and magnify God. Any gift will give you power. Jesus used the same description that it uses in the Old Testament.
Tongues is a lesser gift than prophesy.
If tongues would have been the evidence of the Holy Ghost, Paul wouldn't have rather you prophesy. Tongues here again, covers unknown tongues and other tongues. This is a question that is ask by almost all in the denominations of the Pentecostals. The devil has people believing just the opposite of what the WORD says. Tongues is for them that believe not.