The relation between historic analysis, theoretic reflexion and design works motivates the theoretic and the design science. This means for the theoretic science, that buildings and writings are always seen from the perspective of an architect, to ask project referring questions and make them understandable. In the design science it will be pointed out, in connection with the design decision, the importance of studying the architectural history and reading theoretic writings. In the theoretic lecture it is shown how famous architects always studied the architecture of the past, and criticized the works of their predecessors to acquire design knowledge. In the design works the theory is converted to experience (so far as with) comparative analysis of buildings and projects design decisions can be explained.