While leaving a more detailed description of the composition of Goethe's Entwurf for our next chapter, we shall here deal at once with some of the essential conclusions to which the reader is led in this book. As already mentioned, Goethe's first inspection of the colour-phenomenon produced by the prism had shown him that the phenomenon depended on the presence of a boundary between light and darkness. Newton's attempt to explain the spectrum out of light alone appeared to him, therefore, as an inadmissible setting aside of one of the two necessary conditions. Colours, so Goethe gleaned directly from the prismatic phenomenon, are caused by both light and its counterpart, darkness. Hence, to arrive at an idea of the nature of colour, which was in accord with its actual appearance, he saw himself committed to an investigation of the extent to which the qualitative differences in our experience of colours rests upon their differing proportions of light and darkness.