Having considered the spirit, the field, and the dual method, of mediaeval thought, there remain its classifications of topics. The problem of classification presented itself to Gerbert as one involved in the rational study of the ancient material.[431] But as scholasticism culminated in the twelfth and thirteenth centuries, the problem became one of arrangement and presentation of the mass of knowledge and argument which the Middle Ages had at length made their own, and were prepared to re-express. This ordering was influenced by a twofold principle of classification; for, as abundantly shown by Aquinas,[432] theology in which all is ordered with reference to God, will properly follow an arrangement of topics quite unsuitable to the natural or human sciences, which treat of things with respect to themselves. But the mediaeval practice was more confused than the theory; because the interest in human knowledge was apt to be touched by motives sounding in the need of divine salvation; and speculation could not free itself of the moving principles of Christian theology. On the other hand, an enormous quantity of human dialectic, and a prodigious mass of what strikes us as profane information, or misinformation, was carried into the mediaeval _Summa_, and still more into those encyclopaedias, which attempted to include all knowledge, and still were influenced in their aim by a religious purpose.[433] As the human sciences came from the pagan antique, the accepted classifications of them naturally were taken from Greek philosophy. They followed either the so-called Platonic division, into Physics, Ethics, and Logic,[434] or the Aristotelian division of philosophy into theoretical and practical. The former scheme, of which it is not certain that Plato was the author, passed on through the Stoic and Epicurean systems of philosophy, was recognized by the Church Fathers, and received Augustine’s approval. It was made known to the Middle Ages through Cassiodorus, Isidore, Alcuin, Rabanus, Eriugena and others. Nevertheless the Aristotelian division of philosophy into theoretical and practical was destined to prevail. It was introduced to the western Middle Ages through Boëthius’s Commentary on Porphyry’s _Isagoge_,[435] and adopted by Gerbert; later it passed over through translations of Arabic writings. It was accepted by Hugo of St. Victor, by Albertus Magnus and by Thomas, to mention only the greatest names; and was set forth in detail with explanation and comment in a number of treatises, such as Gundissalinus’s _De divisione philosophiae_, and Hugo of St. Victor’s _Eruditio didascalica_,[436] which were formal and schematic introductions to the study of philosophy and its various branches.