Hume's philosophical writings cast doubt on the truth of church-supported dogmas. Charges of religious heresy permanently barred him from appointment as a professor in Scottish universities. Not only did he deny miracles and other religious dogmas, but his theory of knowledge seemed to undercut the reality of the world itself. He maintained that knowledge came from observation and experience. These, however, were purely individual. A person's perceptions of objects were just that—perceptions. No underlying reality could ever be proved, because every individual's perceptions are his alone—even if they agree with someone else's. The “someone else” is also only a perception of the senses. In his political writings Hume held that government organization, though basically evil, is necessary to guarantee human happiness. In economic theory Hume argued that goods rather than money are the basis of wealth. He believed that each part of the world has special products or services to offer and was an early advocate of increased trade among the nations of the world. Despite the intellectual controversy he aroused, Hume was admired and loved by his many friends, which included members of the clergy. He never married but contented himself with assuring the education of his brother's children.