I think that the gifts of the spirit are always subject to the control of the person who's exercising them. You're not forced in to doing it. Love never forces. And therefore 'the spirit of the prophet is subject to the prophet' is another way it is put. You don't suddenly find yourself taken over by a spirit and find yourself speaking tongues. You're in control, but it's a gift. You can stop and start as you please, but it's a way of communicating with God.