Youcat commented through CCC. Question n. 4 – Part III.

YOUCAT Question n. 4 - Part III. Can we know the existence of God by our reason?

(Youcat answer - repeated) Yes. Human reason can know God with certainty.   

A deepening through CCC

(CCC 32) The world: starting from movement, becoming, contingency, and the world's order and beauty, one can come to a knowledge of God as the origin and the end of the universe. As St. Paul says of the Gentiles: For what can be known about God is plain to them, because God has shown it to them. Ever since the creation of the world his invisible nature, namely, his eternal power and deity, has been clearly perceived in the things that have been made (Rom 1:19-20; cf. Acts 14:15, 17; 17:27-28; Wis 13:1-9). And St. Augustine issues this challenge: Question the beauty of the earth, question the beauty of the sea, question the beauty of the air distending and diffusing itself, question the beauty of the sky… question all these realities. All respond: "See, we are beautiful." Their beauty is a profession [confessio]. These beauties are subject to change. Who made them if not the Beautiful One [Pulcher] who is not subject to change? (St. Augustine, Sermo 241, 2: PL 38, 1134).    

Reflecting and meditating 

(Youcat comment) The world cannot have its origin and its destination within itself. In everything that exists, there is more than we see. The order, the beauty, and the development of the world point beyond themselves toward God. Every man is receptive to what is true, good, and beautiful. He hears within himself the voice of conscience, which urges him to what is good and warns him against what is evil. Anyone who follows this path reasonably finds God.

(CCC Comment)

(CCC 36) "Our holy mother, the Church, holds and teaches that God, the first principle and last end of all things, can be known with certainty from the created world by the natural light of human reason" (Vatican Council I, Dei Filius 2: DS 3004 cf. 3026; Vatican Council II, Dei Verbum 6). Without this capacity, man would not be able to welcome God's revelation. Man has this capacity because he is created "in the image of God" (Cf. Gen 1:27). (End)  

(The next question is:  Why do people deny that God exists, if they can know him by reason?)