O my God,
I firmly believe that thou art one God
in three divine Persons,
Father, Son, and Holy Spirit.
I believe that thy divine Son became man
and died for our sins,
and that he will come to judge the living and the dead.
I believe these and all the truths
which the holy Catholic Church teaches,
because thou hast revealed them,
who canst neither deceive nor be deceived.
Amen.
CATHOLIC TRADITIONAL; CURRENT ENGLISH FORM 17TH-18TH CENTURY AD
The Act of Faith
Also known as O My God, I Firmly Believe
About this prayer
The Act of Faith is one of four traditional Catholic acts of virtue, the others being the Act of Hope, the Act of Love, and the Act of Contrition. Together these four prayers express the theological virtues of faith, hope, and charity, and the penitential disposition needed for a full Christian life. The Act of Faith professes belief in God and in the teachings of the Catholic Church, grounding that belief in God's authority as the source of revelation rather than on personal reasoning alone. These prayers have been part of Catholic devotional life for centuries and are typically taught as part of basic religious instruction. They are said together as a morning offering or as part of a personal prayer routine.
When it's said
The Act of Faith is said as part of the morning offering, before or after Mass, and as a devotional prayer at any time. It is traditionally said together with the Acts of Hope, Love, and Contrition. In the Liturgy of the Hours it is not prescribed, but it appears in Catholic prayer books as a standard daily devotion.
Notes on the text
The phrase 'who canst neither deceive nor be deceived' is a traditional formulation of divine infallibility: God cannot lie and cannot be mistaken, therefore what God reveals can be trusted absolutely. The prayer grounds faith in God's authority rather than in the credibility of human witnesses.
Source
Traditional Catholic prayer, 17th-18th century English form. Text from F.X. Lasance, The Blessed Sacrament Book, 1913. Public domain.
Last reviewed: May 2026 against primary source.