He who says consciousness says science, or at least, the beginning of science. Consciousness implies a representation. In other words, no modification of the ego becomes conscious except by awakening in the mind a representative image of the object that has produced it and of the relation of that object to the ego. All our sensations and all our feelings are accompanied by images. The religious sentiment does not attain to the light of consciousness in any other way. It is because it is a state or conscious movement of the soul that it becomes, it also, a principle of knowledge. No kind of mental life begins with clear and abstract ideas. An idea is derived from an image, and, in order to produce the image, an external or an internal impression is necessary. It is true that the idea or the image has, in its turn, the mysterious power of reproducing and renewing the sensation or the feeling from which it sprang. On this is based the art of teaching and the power of tradition. But this must not be allowed to produce in us the illusion that originally the idea preceded the sensation. The development of the mental life of children is proof of the contrary. We only know that by which we or our kind have been in some degree affected. Our ideas are simply the algebraic notation of our impressions and movements. That which is outside our life is outside our view. Without the external sensations which represent the action of the world on the ego, we should have no knowledge of the world. Without the subjective reaction of the ego against that action of the world, a reaction which manifests itself in the moral, aesthetic, and religious life of the soul, we should have no moral or religious idea, no notion of the good or the beautiful. All our metaphysical ideas come from that source. It remains, of course, to inquire what is the worth of ideas of this order. It is the particularly complex and delicate question that we here approach. There is no serious philosophy to-day that does not start with a theory of knowledge. Religious knowledge cannot escape by any special privilege. The criticism of it is all the more necessary, because illusion, in this matter, is so easy, and because it clothes itself in a sacred character. The theologian who undertakes the scientific treatment of dogmas without first measuring the scope of the instrument he employs, and estimating the worth of the materials he uses, knows not what he is doing. 1. _Obsolete Theories of Knowledge_ Formerly three explanations of our knowledge prevailed in philosophy: the hypothesis of a primitive revelation; the idealist theory; and the sensualist theory.