Coinciding with the scientific flourishing of the 5th / 11th century, which was favoured by the cultural policy of the Andalusī kingdoms ( mulūk al-tawā'if ), Abū ‘ Umar ibn ‘ Abd al-Barr, Ibn Hazm and Sā‘ id al-Andalusī all dealt with the classification of the sciences in many works that are already known. Ibn Bājja began his career at the end of this period. In his glosses to al-Fārābī’s commentary to the Isagoge he wrote a text on this subject that has not yet been analysed. The present paper studies Ibn Bājja's classification in connection with his predecessors and with the scientific and philosophical background of Andalusī culture. In their classifications of the sciences, all these authors express and stress important factors of the evolution of Andalusī science and thought, such as the dialectic between religious and rational sciences and the importance of the scientific method derived from Aristotle's logic. Sā‘ id al-Andalusī and Ibn Bājja ( and, to a lesser extent, Ibn Hazm ) show the profound influence exerted by al-Fārābī’s works, particularly the Ihsā' al-‘ ulūm. Thus, Ibn Bājja foreshadows the evolution of sciences in the next century and the movement headed by Ibn Rushd, Ibn Tufayl and others, characterized by the search for concordance with the postulates set forth by philosophical disciplines.