the system of St. Thomas Aquinas teaching that philosophy and theology have separate spheres with one seeking truth through the agency of reason and the other through that of revelation but reaching conclusions that support each other, that all knowledge begins with sense perception from the data of which the intellect abstracts universals and on the basis of these proceeds through deduction and induction to science or knowledge of things in their causes and thence to knowledge of ultimate causality and the conclusion that the universe is the creation of an infinite uncreated Being, that everything in nature is composed of matter and form with the potentiality of the former being brought to actuality by the latter, that everything that is natural is good in itself and a cause of evil only when used for ends other than those for which it was created or beyond the limits prescribed by sound reason or divine law, and that because of his rational nature man is compelled by necessity to seek the highest good.
doctrines of Thomas Aquinas, medieval Dominican Theologian, concerning the nature of knowledge and the nature of God's presence in the universe. More information here.
Thomism is the philosophical school that followed in the legacy of Thomas Aquinas. The word comes from the name of its originator, whose summary work Summa Theologiae has arguably been second only to the Bible in importance to the Catholic Church. In the Encyclical Doctoris Angelici, Pius X cautioned that the teachings of the Catholic Church cannot be understood scientifically without the basic philosophical underpinning of Aquinas's major theses.