How did St. Thomas Aquinas distinguish philosophy from theology?

St. Thomas Aquinas distinguished between philosophy and theology based on their distinct domains, methods, and starting points.1

• Domains and Methods: The philosopher seeks the first causes of things by beginning with data furnished by the senses, relying solely on the natural light of reason. Conversely, the theologian’s inquiry focuses on God as revealed in sacred scripture.12
• Authority: In theology, an appeal to authority carries the most weight, whereas in philosophy, it carries the least.1
• Nature of Knowledge: Aquinas viewed theology as a "science" in the Aristotelian sense—knowledge rationally derived from propositions accepted as certain because they are revealed by God. While reason can operate within faith, the theologian accepts faith and authority as the starting point before proceeding to conclusions through reason.2

Aquinas maintained that reason and faith cannot contradict each other because both originate from the same divine source. He argued that revelation supplements, rather than replaces, the findings of sound philosophy, allowing for a harmonious integration of natural knowledge and Christian belief.13