Summa Theologiae
       St. Thomas Aquinas
       
       This beginners' textbook in theology, never finished by
       St. Thomas Aquinas, sets out to summarize the entirety of
       sacred theology.  Used as the primary teacher of sacred
       theology in seminaries for centuries, it had the unique
       privilege of being kept open on the altar during the Council
       of Trent, so that the fathers of the Council could always
       and immediately draw from its wisdom, the only book besides
       the Sacred Scriptures themselves accorded this honor.  The
       great Leo XIII, of happy memory, stated in his encyclical
       Aeterni Patris that St. Thomas Aquinas should be the
       basis for any Catholic philosophical and theological
       education, and this is the greatest of St. Thomas's works.
       Its value cannot be overstated.
       
 (HTM) Prima Pars (PDF) (free)
 (HTM) Prima Secundæ (PDF) (free)
 (HTM) Secunda Secundæ (PDF) (free)
 (HTM) Tertia Pars (PDF) (free)