 In the Latin West, Averroes’ explanation dominated the discussion for several centuries (Hasse 2007a). Thomas Aquinas argues that there is no need to assume the existence of an Avicennian giver of forms to explain spontaneous generation, since the celestial power suffices for producing ordinary animals from matter. More complex beings, however, such as horses and human beings, cannot be produced by the celestial power alone without the formative power of the semen (Quaest. de potentia, qu. 3 a. 8,9,11). Thomas’ position was called the media via by later authors, that is, the middle way between Avicenna and Averroes, since Thomas rejected Avicenna’s theory, but also modified Averroes’ position in treating spontaneous generation as a natural, and not a miraculous phenomenon.