 Making use of the medical and philosophical knowledge available to him, Kilwardby argues that the semen cannot be just a superfluity of digested food because in that case the offspring would resemble the father’s aliment and not the father (E 4, 30). In addition to the role played by the father in the generation of the new being, the mother contributes to the offspring with matter that is used to protect and feed the embryo (some matter of the semen has the same purpose) and the local warmth that constitutes the proper environment to the development of the new life.