 Once his defense of the use of final causes is firmly in place, Aristotle can make a step further by focusing on the role that matter plays in his explanatory project. Let us return to the example chosen by Aristotle, the regular growth of sharp teeth in the front and broad molars in the back of the mouth. What explanatory role is left for the material processes involved in the natural process? Aristotle does not seem to be able to specify what material processes are involved in the growth of the teeth, but he is willing to recognize that certain material processes have to take place for the teeth to grow in the particular way they do. In other words, there is more to the formation of the teeth than these material processes, but this formation does not occur unless the relevant material processes take place. For Aristotle, these material processes are that which is necessary to the realization of a specific goal; that which is necessary on the hypothesis that the end is to be obtained.