Atheist
Why believe in God at all?
Reason itself points to God as the necessary cause of a contingent universe, the source of objective moral order, and the ground of the intelligibility we find everywhere in nature — a conclusion Scripture affirms but does not depend on faith alone to reach.
Catholic teaching
The Church teaches that God's existence can be known with certainty from creation by the natural light of human reason, even before divine revelation, though revelation brings this knowledge to fullness and intimacy through Christ.
Biblical foundation
Paul argues that what can be known about God 'has been shown' to all people because 'his eternal power and divine nature, have been clearly perceived in the things that have been made,' leaving humanity 'without excuse' (Rom 1:19-20).
Scripture references
Historical evidence
Classical arguments for God's existence developed by figures such as Aristotle, and later refined by St. Thomas Aquinas in his Five Ways in the thirteenth century, continue to be seriously discussed and defended in academic philosophy of religion today.
The Church Fathers
“Therefore there must exist something that is of itself necessary, not receiving its necessity from another, but rather causing in others their necessity. This all men speak of as God.”