În prealabil postat de Mihnea Dragomir

The sacrosanct Roman Church, founded by the voice of our Lord and Savior, firmly believes, professes, and preaches one true God omnipotent, unchangeable, and eternal, Father, Son, and Holy Ghost; one in essence, three in persons; Father unborn, Son born of the Father, Holy Spirit proceeding from Father and Son; that the Father is not Son or Holy Spirit, that Son is not Father or Holy Spirit; that Holy Spirit is not Father or Son; but Father alone is Father, Son alone is Son, Holy Spirit alone is Holy Spirit. The Father alone begot the Son of His own substance; the Son alone was begotten of the Father alone; the Holy Spirit alone proceeds at the same time from the Father and Son. These three persons are one God, and not three gods, because the three have one substance, one essence, one nature, one divinity, one immensity, one eternity, and all these things are one where no opposition of relationship interferes .

(Cantate Domino)
În bold sunt cuvintele care arată caracterul infailibil al documentului.
Deci, avem întrunite următoarele mărci ale infailibilităţii papale:
-este document semnat de papa în mod personal (nu prin delegaţi)
-se referă la chestiuni de credinţă sau morală
-există forumulare solemnă: aceasta este credinţa Bisericii, nu părerea personală a papei.

Pentru neclarităţi privind cine este capul Bisericii şi care sunt condiţiile infailibilităţii, consultaţi clarificările aduse de Conciuliul Vatican I.