Certainty refers to the three certainties required for a trust to be valid. In the first place he preaches certainties and not doubts. Niklas Luhmann used cybernetics to challenge the role of foundational unities and canonical certainties. His autobiography, "Certainties and Doubts&colon; A Philosophy of Life", was published in 2001. He emphasized the law's historical and human dimensions rather than its certainties and extremes. Celan's profound spiritual doubt contrasts with U2 members' previous religious certainties. Mathematics concretise constant certainties via formulae; painting does it via colours. In part, this has been attributed to the desire for ethical certainties. It belongs to the domain of constant certainties and is under the control of logic. He formulated a legal test, now known as the "three certainties".