The self-contained being of ideas is not thought of by the naïve mind as real in the same sense. An object conceived "merely in idea" is regarded as a chimera until sense-perception can furnish proof of its reality. In short, the naïve man demands, in addition to the ideal evidence of his thinking, the real evidence of his senses. In this need of the naïve man lies the ground for the origin of the belief in revelation. The God whom we apprehend by thought remains always merely our idea of God. The naïve consciousness demands that God should manifest Himself in ways accessible to the senses. God must appear in the flesh, and must attest his Godhead to our senses by the changing of water into wine. Even knowledge itself is conceived by the naïve mind as a process analogous to sense-perception. Things, it is thought, make an impression on the mind, or send out copies of themselves which enter through our senses, etc. What the naïve man can perceive with his senses he regards as real, and what he cannot perceive (God, soul, knowledge, etc.) he regards as analogous to what he can perceive. On the basis of Naïve Realism, science can consist only in an exact description of the content of perception. Concepts are only means to this end. They exist to provide ideal counterparts of percepts. With the things themselves they have nothing to do. For the Naïve Realist only the individual tulips, which we can see, are real. The universal idea of tulip is to him an abstraction, the unreal thought-picture which the mind constructs for itself out of the characteristics common to all tulips.