Youcat commented through CCC. Question n. 36.

YOUCAT Question n. 36 - Can we deduce logically that God is triune?

(Youcat answer) No. The fact that there are three persons (Trinity) in one God is a mystery. We know only through Jesus Christ that God is Trinitarian.         

A deepening through CCC

(CCC 237) The Trinity is a mystery of faith in the strict sense, one of the "mysteries that are hidden in God, which can never be known unless they are revealed by God" (Dei Filius 4: DS 3015). To be sure, God has left traces of his Trinitarian being in his work of creation and in his Revelation throughout the Old Testament. But his inmost Being as Holy Trinity is a mystery that is inaccessible to reason alone or even to Israel's faith before the Incarnation of God's Son and the sending of the Holy Spirit.     

Reflecting and meditating 

(Youcat comment) Men cannot deduce the fact that God is a Trinity by means of their own reason. They acknowledge, however, that this mystery is reasonable when they accept God’s Revelation in Jesus Christ. If God were alone and solitary, he could not love from all eternity. In the light of Jesus we find already in the Old Testament (for example, Gen 1:2; 18:2; 2 Sam 23:2), indeed, even in all of creation, traces of God’s Trinitarian Being.

(CCC Comment)

(CCC 261) The mystery of the Most Holy Trinity is the central mystery of the Christian faith and of Christian life. God alone can make it known to us by revealing himself as Father, Son and Holy Spirit. (CCC 50) By natural reason man can know God with certainty, on the basis of his works. But there is another order of knowledge, which man cannot possibly arrive at by his own powers: the order of divine Revelation (Cf. Dei Filius DS 3015). Through an utterly free decision, God has revealed himself and given himself to man. This he does by revealing the mystery, his plan of loving goodness, formed from all eternity in Christ, for the benefit of all men. God has fully revealed this plan by sending us his beloved Son, our Lord Jesus Christ, and the Holy Spirit. (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). 

(The next question is: Why is God “Father”?)