Sacred theology considers principles and parts; a principle is incomplex or complex

Chapter 2. On the principles of sacred theology, and specifically on the first and last complex principle.

I. Sacred theology asks us to weigh two things: the principles from which the discipline is drawn, and the parts into which it is divided.

II. By principles of sacred theology we mean those propositions that let us deduce the sacred dogmas of the Christian faith by ordered discourse — and then resolve the deduced dogmas back into the same propositions — so that a sound, modest, God-fearing person may rightly give assent.

Taken generally, a principle is whatever something proceeds from in any way (Thomas, Summa Theologiae I, q. 33, art. 1). Principles are either simple or complex. A simple principle is a simple term, either principal or less principal. The principal term is God himself — which is to say, Christ — of whom (1 Corinthians 1:30) speaks. Fulgentius writes to Thrasamund (p. 108): Christ is the beginning, for as everlasting he goes before; Christ is the end, for as perpetual he closes all things. Christ is the beginning, for he himself began; Christ is the end, for he perfects. The less principal term is the Word of God, the instrument through which the Holy Spirit converts, illuminates, and saves (Romans 1:16; compare 1 Corinthians and related places).

With those two incomplex principles in place, we turn to the first complex principle: a whole proposition from which a conclusion follows by logic. Some therefore call it a logical principle, or a principle of cognition, because our logical deduction of what we believe starts here, and demonstration cannot climb beyond this first and most general point. The complex principle holds together two respects at once — the respect from which, namely God's infallible testimony, and the respect under which, namely the light of revelation — and so is called a principle from which and under which. That sets it far apart from an exterior principle, which only occasions our knowledge of faith and is a necessary condition without which faith does not arise (today, for example, the parental authority that plants saving truth in us: 2 Timothy 3:15), and also far apart from a motive principle, which is only a topical or probable argument, such as a miracle.

A Christian does not depend on those lesser supports. They win only the assent of human apprehension — Bellarmine himself grants as much. What then is our principle? It is apodictic and indemonstrable, worthy of faith from itself, and such that falsehood cannot underlie it in any way. Still, a necessary condition must be joined to it — hearing or reading — which is why Scripture calls it the word of hearing (1 Thessalonians 2:13). I am speaking of the dogmas of faith as they reach us from outside. Dogmas come in two kinds: some for believing, others for knowing. The first kind is known by God's special revelation; the second lies open under the light of reason. The first is believed; the second is known. Our subject here is properly the former. Propositions that do not properly belong to faith — and some such do appear in the Bible — fall outside this account.