Philosophy is the love of wisdom. In application, it is the study of the first principles and the ultimate causes of all knowable reality. In the classical world, it was the highest science. Later, the scholastics made this natural wisdom subservient to the supernatural wisdom of revelation, calling itt “the handmaid of theology” (ancilla theologiae). So many of the dogmas of our Faith are defined more clearly with the help of philosophical terms that have been perennially upheld by the greatest thinkers of the West: substance, accident, nature, essence, existence, hypostasis, matter, form, genus, species, cause, principle, and relation, to name the more commonly used.
Traditionally, philosophy is divided into seven disciplines: logic, cosmology, history of philosophy, psychology, ethics, epistemology, and ontology.
Logic is the science and art of correct reasoning. Cosmology is the study of matter in motion and material change. Psychology is the study of life and the principle of life, the soul. (Today it is relegated to the study of abnormal mental behavior, a far cry from its traditional subject of inquiry.) Ethics is the study of human acts as to their moral rectitude or lack thereof. Epistemology is the study of knowledge. How is it that something outside the mind is abstracted into the mind? Ontology, the highest of the philosophic sciences, is the study of being as being. What is the difference between essence and existence? Ontology is also called metaphysics.