This chapter discusses the central question why Aristotle, in spite of having everything required to conceptualize a complex measure of speed in terms of time and space, did in the end not explicitly develop such a measure. It is first investigated whether contemporaries of Aristotle may have worked with such a complex measure of speed, and concluded that it cannot be found in either of the two thinkers most likely to have done so, namely Eudoxus and Autolycus. The second part of the chapter investigates what made Aristotle cling to a simple measure and suggests that there are mathematical and metaphysical reasons: metaphysically, Aristotle cannot explicitly accommodate a relation as a measure of motion, since relations are derivative and problematic for him; mathematically, the principle of homogeneity which derives from the realm of Greek mathematics makes it impossible to combine of different dimensions in a single measure in the way needed for measuring speed in a mathematically informed physics such as Aristotle’s.