Theory of Colours (original German title Zur Farbenlehre) is a book by Johann Wolfgang von Goethe about the poet's views on the nature of colours and how these are perceived by humans. Published in 1810, it contains detailed descriptions of phenomena such as coloured shadows, refraction, and chromatic aberration. Goethe's book provides a catalogue of how colour is perceived in a wide variety of circumstances, and considers Isaac Newton's observations to be special cases. Unlike Newton, Goethe's concern was not so much with the analytic treatment of colour, as with the qualities of how phenomena are perceived. Philosophers have come to understand the distinction between the optical spectrum, as observed by Newton, and the phenomenon of human colour perception as presented by Goethe-a subject analyzed at length by Wittgenstein in his exegesis of Goethe in Remarks on Colour.