Aristotle's Metaphysics 2 consists of two chapters on methodology flanking an important discussion of the impossibility of infinite causal chains. The subject is vital for scientific method and for theological belief in a first cause and in a beginning of the universe. Philoponus later attacked Aristotle on this last point, but Alexander presents Aristotle's view in a most favourable light. In Metaphysics 3, Aristotle sets out what he sees as the central problems of metaphysics. Alexander's commentary was subsequently used by the Neoplatonists, two of whom have left their own commentaries, so that Alexander's Aristotelian interpretation can be compared with its rivals.