Internal criterion of the thing: inspiration; prophetic holiness and infallibility in writing
The internal criterion is of the thing or of the sign. The criterion of the thing is God's immediate inspiration, calling, and instruction (2 Timothy 3:16; 2 Peter 1:20; Luke 16:29; Ephesians 2:20; Hebrews 1:1; Galatians 1 and 11-12, 15-16; Romans 15:18) — of him who wrote the Scriptures with God inspiring, indeed by whose hands God himself wrote, as Alphonsus de Castro speaks, Against Heresies book 1 chapter 2 page 4.
From which we gather: (1) that the prophets or canonical writers have holiness in living (2 Peter 1:21) — not a holiness that means absolute impeccability (1 Kings 8:46; 2 Chronicles 6:36; Ecclesiastes 7:21; Proverbs 20:9), but one that excludes voluntary sins, malice, stubbornness, and an evil purpose — that is, sins against conscience (1 John 3).
(2) The same men's infallibility in writing, because he writes not as a man but as a holy man of God (2 Peter 1:21), led by the Spirit of truth into all truth (John 14:17; John 16:13; 2 Peter 1:21) — by the example of converted David (Matthew 22:43; Psalm 45:2; 2 Samuel 23:2). For if error and falsehood were admitted into so high a summit of authority, no particle of these books would remain that could not be called into doubt, as Augustine well warns in Letter 8 to Jerome.
Therefore, that the Evangelists' writings may stand as canonical and authentic and their authority remain safe, every falsehood ought to be absent from them — not only what is put forward by lying, but also what comes by forgetting — as the same teaches in On the Harmony of the Gospels book 1 chapter 12. Yet judgment about the prophets' infallibility is to be made from the truth of God which they reveal dogmatically, not from the history of a deed and of a speech which they sometimes recount as in character, as Genesis 3:1, Genesis 3:4-Genesis 3:5; John 8:44 — according to Ruiz's rule 219: an evangelical narrative, though most true, yet not all things said there are believed to be true, from Augustine, Against the Priscillianists chapter 9.
Latin
Internum est rei aut signi. Momentum rei est immediata Dei inspiratio, vocatio & eruditio, 2. Tim. 3.v.16. 2. Pet. 1.v.20. Luc. 16.v.29. Eph. 2.v.20. Heb. 1.v.1. Gal. 1. & 11.12.15.16. Rom. 15.v.18. ejus, qui Deo inspirante scripturas scripsit, imo cujus manibus Deus ipse scripsit, ut loquitur Alphonsus de Castro, lib. 1. adv. haeres. c. 2. p. 4. Unde colligimus, 1. prophetas seu canonicos scriptores sanctimonia in vivendo, 2. Pet. 1.v.21. non quae omnimodam anamartesiam impeccantiam dicat, 1. Reg. 8.v.46. 2. Chron. 6.v.36. Eccles. 7.v.21. Prov. 20.v.9. sed quae peccata voluntaria, malitiam, contumaciam & propositum malum, seu peccata contra conscientiam, excludat, 1. Joh. 3. 2. Ejusdem infallibilitatem in scribendo, quia scribit, non ut homo, sed ut sanctus Dei homo, 2. Pet. 1.v.21. a spiritu veritatis ductus in omnem veritatem, Joh. 14.v.17. 16.v.13. 2. Pet. 1.v.21. exemplo Davidis conversi, Matth. 22.v.43. ps. 45.v.2. 2. Sam. 23.v.2. Admisso enim in tantum autoritatis fastigium errore ac mendacio, nulla horum librorum particula manebit, quae non posset in dubium vocari, ut bene monet Augustinus ep. 8. ad Hieron. Quapropter, ut canonica & authentica Euangelistarum scriptis constet & salva maneat autoritas, omnis ab illis abesse debet falsitas, non solum ea quae mentiendo promitur, sed etiam ea quae obliviscendo, ut idem docet lib. 1. de cons. Euang. cap. 12. Est tamen de prophetarum infallibilitate judicandum e veritate Dei, quam dogmatice revelant, non ex historia facti, sermonisque quem interdum hypocriticos recensent, ut Gen. 3.v.1.4.5. Joh. 8.v.44. juxta regulam CCXIX. Ruizii: Euangelica enarratio quamvis verissima sit, non tamen omnia, quae ibi dicuntur, vera esse creduntur, ex Augustino lib. contra Priscillianistas cap. 9.