Abstract 1. 1. An analysis of the tongue function and its working spaces is submitted. 2. 2. The dorsum of the tongue in its reference position to the tooth plane is discussed. 3. 3. A more detailed study of the alteration and redistribution of the tongue and vestibular space is suggested. 4. 4. A functional classification of tongues affords information necessary for adequate prognosis in dental prosthesis. 5. 5. Methods of increasing tongue space are suggested. 6. 6. The tongue factor in speech is outlined.