It is impossible to study the development of Christian thought on marriage without reference to St. Augustine. The many-faceted and nuanced character of Augustinian thinking in this field is probably to be attributed not so much to Augustine's personal experience in sexual matters as to his having been involved over some forty years in very particular and very contrasting controversies concerning matrimony. The earlier part of his Catholic life saw him engaged in conflict with the pessimism of the Manicheans; in his later years he combated the naturalistic optimism of the Pelagians. The Manicheans saw marriage and procreation as major expressions of material and bodily creation and hence as evil; Augustine defended the goodness of both. The Pelagians, in their excessive optimism about man's present state, took little or no account of the disordered element now strongly present in sex, also in conjugal sexuality; and Augustine sought to alert people to this disorder.[17]