The associative imagination is first formally introduced ( Works, 4.236) by Ruskin in Modern Painters II (1846), but its development was influenced by his earlier concept of the unity of the Liber Studiorum, as a coherent system of inter-related images and ideas; see Ruskin's introduction to the Liber Studiorum. He discusses, as an important example of the associative imagination, the Liber Studiorum plate Procris and Cephalus, explaining that he knows 'of no landscape more purely or magnificently imaginative, or bearing more distinct evidence of the relative and simultaneous conception of the parts' ( Works, 4.425).