In this paper, relying on the formal framework provided by one of the most recent design theories, C-K theory, we analyse the historical development of design theories in the particular case of German systematic design. We study the three moments in the development of design theories (1850, 1900 and 1950). The analysis leads to the three main research conclusions regarding design theorizing. (1) The development of design theories and methods corresponds to specific rationalizations of the design activity in historical contexts, characterized by types of products, science and knowledge production capacities. (2) While engineering sciencesmodel known objects, design theories support reasoning on unknown objects. (3) Design methods do not target single innovations but aim to improve collective design capacities. Their performance can be assessed by the types of new objects they help design (generative capacity) and in terms of the capacities required by their users (conjunctive capacity). Historically, systematic design emerged as a formal framework with particularly strong generative and conjunctive capacities.