Question: Which philosopher is quoted by the Catechism?
Sentence: While the term "law" is never explicitly defined in the Code, the Catechism of the Catholic Church cites Aquinas in defining law as "...an ordinance of reason for the common good, promulgated by the one who is in charge of the community" and reformulates it as "...a rule of conduct enacted by competent authority for the sake of the common good."
Answer in sentence: yes