contemplation. Of particular interest to 20th-century music theorists is the attention he paid to silence as an integral part of music. Metaphysics of morals Both of his early treatises, De natura boni and De bono, start with a metaphysical investigation into the concepts of the good in general and the physical good. Albert refers to the physical good as bonum naturae. Albert does this before directly dealing with the moral concepts of metaphysics. In Albert's later works, he says in order to understand human or moral goodness, the individual must first recognize what it means to be good and do good deeds. This procedure reflects Albert's preoccupations with neo-Platonic theories of good as well as the doctrines of Pseudo-Dionysius. Albert's view was highly valued by the Catholic Church and his peers. Natural law Albert devoted the last tractatus of De Bono to a theory of justice and natural law. Albert places God as the pinnacle of justice and natural law. God legislates and divine authority is supreme. Up until his time, it was the only work specifically devoted to natural law written by a theologian or philosopher. Friendship Albert mentions friendship in his work, De bono, as well as presenting his ideals and morals of friendship in the very beginning of Tractatus II. Later in his life he published Super Ethica. With his development of friendship throughout his work it is evident that friendship ideals and morals took relevance as his life went on. Albert comments on Aristotle's view of friendship with a quote from Cicero, who writes, "friendship is nothing other than the harmony between things divine and human, with goodwill and love". Albert agrees with this commentary but he also adds in harmony or agreement. Albert calls this harmony, consensio, itself a certain kind of movement within the human spirit. Albert fully agrees with Aristotle in the sense that friendship is a virtue. Albert relates the inherent metaphysical contentedness between friendship and moral goodness. Albert describes several levels of goodness; the useful (utile), the pleasurable (delectabile) and the authentic or unqualified good (honestum). Then in turn there are three levels of friendship based on each of those levels, namely friendship based on usefulness (amicitia utilis), friendship based on pleasure (amicitia delectabilis), and friendship rooted in unqualified goodness (amicitia honesti; amicitia quae fundatur super honestum). Cultural references The iconography of the tympanum and archivolts of the late 13th-century portal