The intellectual faculty, i.e. thought, reason. For St. Thomas, reason or intellect is man s greatest treasure, that which raises him above the animals. Ultimately, we do need direct, intuitive knowledge of God. Reason depends on sensory experience, and sensory experience is of matter, not spirit. So reason, like all things human, is imperfect, and cannot comprehend the perfection that is God.
Faith is our ultimate refuge.
Nevertheless, he insisted, faith and reason do not conflict, since God would not have made a world that did not ultimately match up with revealed truth. He also devoted a significant portion of the Summa to angels and demons, which he thought of as every bit as real as anything else. Among other things, he believed that the angels moved the planets, that they had no bodies, that they moved instantaneously, and that each person had his or her very own guardian angel. His ideas threatened many in the church, most especially the Franciscans. His works emphasized reason too much and faith too little.