Full Idea
Since the speculative reason is concerned chiefly with necessary things, which cannot be otherwise than they are, its proper conclusions, like the universal principles, contain the truth without fail.
Gist of Idea
The conclusions of speculative reason about necessities are certain
Source
Thomas Aquinas (Summa Theologicae [1265], I-II Q94 4)
Book Reference
Aquinas,Thomas: 'On Law, Morality and Politics', ed/tr. Baumgarth,W. /Regan R. [Hackett 1988], p.51
A Reaction
This seems over-confident, and to confuse the facts with our knowledge of the facts. Simple arithmetic may seem certain, but long and intricate proofs are always a little uncertain.