1. Having spoken of sensations, we come now to ideas. We must, however, before making this transition, inquire if there be in our mind ought else than sensation, if all the inward phenomena which we experience be ought else than sensations transformed. Man, when he rises from the sphere of sensations, from those phenomena which place him in relation with the external world, meets a new order of phenomena, of whose presence he is equally conscious. He cannot reflect upon sensations without being conscious of something more than sensation; nor on the recollection or the inward representation of sensations, without discovering something distinct both from the recollection and from the representation. 2. According to Aristotle, there is nothing in the understanding which has not first been in the senses; and the schools have for long ages re-echoed this thought of the philosopher: _nihil est in intellectu quod prius non fuerit in sensu_. The order, therefore, of human knowledge, is from the external to the internal. Descartes pretended that we ought to invert this order, and proceed from the internal to the external. Malebranche, his disciple, went farther, and was of opinion that the understanding, enfolded in itself, should hold only the least possible intercourse with the external world. According to him, no atmosphere is so fatal to intellectual health as that of the world of the senses; sensations are an inexhaustible fountain of error, and the imagination is an enchantress only the more dangerous because she has fixed her dwelling at the very portal of the intellect, which, with her seductive beauty and gorgeous ornaments, she hopes to rule at her pleasure. 3. Locke strove to rehabilitate the old Aristotelian maxim, joined, however, to the criterion of observation: besides sensation he admitted only reflection, but he taught that the mind was endowed with innate faculties. His disciple, Condillac, not satisfied with this, taught that all the actions of our mind were simply sensations transformed: instead of distinguishing with Locke two sources of our ideas, the senses and reflection, he thought it more exact to admit only one, as well because reflection is in its root only sensation, as because it is rather the channel by which ideas originating in the senses pass, than their source. Judgment, reflection, desires, and passions are in Condillac's estimation nothing else than sensation transformed in various modes. It seemed to him, therefore, very idle to suppose the mind to have received immediately from nature the faculties with which it is endowed. Nature has given us organs which show us by pleasure or pain what we ought to seek or to avoid; but here she stops, and leaves to experience the task of leading us to contract habits and finish the work she has commenced.[1] [1] _Traité des Sensations._ Préface.