 The first line of the third quatrain extends the conceit of the Platonic theory, the idea that the perceptions of reality are merely reflections of the essential reality of forms.Platonic theory suggests that our perceptions are derived from this world of forms in the same way shadows are derived from the objects that are lit.The metaphor of shadow was often employed to help explain the illusory quality of perception and the reality of forms, both by Renaissance Platonists and by Plato himself in his book, Symposium.