 Aristotle was not the first thinker to engage in a causal investigation of the world around us. From the very beginning, and independently of Aristotle, the investigation of the natural world consisted in the search for the relevant causes of a variety of natural phenomena. From the Phaedo, for example, we learn that the so-called “inquiry into nature” consisted in a search for “the causes of each thing; why each thing comes into existence, why it goes out of existence, why it exists” (96 a 6–10). In this tradition of investigation, the search for causes was a search for answers to the question “why?”. Both in the Physics and in the Metaphysics Aristotle places himself in direct continuity with this tradition. At the beginning of the Metaphysics, Aristotle offers a concise review of the results reached by his predecessors (Metaph. I 3–7). From this review we learn that all his predecessors were engaged in an investigation that eventuated in knowledge of one or more of the following causes: material, formal, efficient and final cause. However, Aristotle makes it very clear that all his predecessors merely touched upon these causes (Metaph. 988 a 22–23; but see also 985 a 10–14 and 993 a 13–15). That is to say, they did not engage in their causal investigation with a firm grasp of these four causes. They lacked a complete understanding of the range of possible causes and their systematic interrelations. Put differently, and more boldly, their use of causality was not supported by an adequate theory of causality. According to Aristotle, this explains why their investigation, even when it resulted in important insights, was not entirely successful.