Book VI of the "Republic" identifies the highest form as the Form of the Good, the cause of all other Ideas, and that on which the being and knowing of all other Forms is contingent. Conceptions derived from the impressions of sense can never give us the knowledge of true being; i.e. of the forms. It can only be obtained by the soul's activity within itself, apart from the troubles and disturbances of sense; that is to say, by the exercise of reason. Dialectic, as the instrument in this process, leading us to knowledge of the forms, and finally to the highest form of the Good, is the first of sciences. Later Neoplatonism, beginning with Plotinus, identified the Good of the "Republic" with the transcendent, absolute One of the first hypothesis of the "Parmenides" (137c-142a).