Abstract
This analysis of Ptolemy's Teatriblos deals with how the social and cultural role of astrology changed between lì and III century a D.: from a practice hard fought, although successful, to a generally accepted branch of knowledge. In Ptolemy's treatise astrology is shown to be not a science but an art: a techne" fallible but not controvertible. As the basis for such a project of reforming common opinion about astrol¬ogy, we find a quiet yielding attitude toward sceptical antidogmatism, and a non-deterministic way of conceiving man 's naturai relationship with heavenly bodies.