The Mutus Liber is an epistemological treatise. The alchemical laboratory is the mind. In it, thoughts are chemical compounds and their processes are reactions producing knowledge. The operation works on the mind. The alchemical transmutation takes place in the mind, by the mind and through the mind in all its stages, conscious, subconscious, unconscious and beyond. Therefore, the key to interpret the plates and to open the mouth of the Mute Book is gnoseological. The chemical elements, consequently, are only metaphors to describe the epistemic process.