|Aquinas Day By Day|
Aquinas’s topic: logic of arguments: scientific knowledge
Church calendar: Death of Thomas Aquinas at Fossanova, Italy, south of Rome; traditional feast day.
Aquinas’s text: Expositio libri Posteriorum , Bk. 1, lec. 4
Since the purpose of demonstration is to attain “science [Greek: episteme; Latin: scientia], Aristotle defined scientific knowledge. Here is Br. Thomas’s explanation of that definition, which shows that the classic sense of “science” is wider than but includes the modern sense of this term. For Aquinas, scientific knowledge is causal knowledge, it is knowledge of the causes of a definite effect, and it is causal knowledge that is certain.
Then (71b10) [Aristotle] posits his definition of scientific knowing in the absolute sense. Concerning this one ought to realize that to “know something scientifically” is to know it completely, that is, completely to apprehend its truth. For the principles of the being of a thing are the same as those of its truth, as is stated in Metaphysics 2. Therefore, the scientific knower, if he is to know completely, must understand the cause of the thing known. But if he were to know only the cause, he would not yet know the effect actually—which is knowing absolutely—but only virtually—which is knowing “in a qualified sense” and “accidentally.” Therefore, it is necessary that the scientific knower know “absolutely,” including the application of the cause to the effect. And since science is also certain knowledge of the thing, while a thing that could be otherwise no one can know with certainty, it is further necessary that what is scientifically known could not be otherwise. Therefore, because science is complete knowledge, he says, “When we think that we know the cause,” but because it is actual knowledge through which we know scientifically in the full sense, he adds “as the cause of that fact,” and because it is certain knowledge, he adds, “and that the fact could not be other than it is (71b11).”
Secundo, cum dicit: cum causam arbitramur etc., ponit definitionem ipsius scire simpliciter. Circa quod considerandum est quod scire aliquid est perfecte cognoscere ipsum, hoc autem est perfecte apprehendere veritatem ipsius: eadem enim sunt principia esse rei et veritatis ipsius, ut patet ex II metaphysicae. Oportet igitur scientem, si est perfecte cognoscens, quod cognoscat causam rei scitae. Si autem cognosceret causam tantum, nondum cognosceret effectum in actu, quod est scire simpliciter, sed virtute tantum, quod est scire secundum quid et quasi per accidens. Et ideo oportet scientem simpliciter cognoscere etiam applicationem causae ad effectum. Quia vero scientia est etiam certa cognitio rei; quod autem contingit aliter se habere, non potest aliquis per certitudinem cognoscere; ideo ulterius oportet quod id quod scitur non possit aliter se habere. Quia ergo scientia est perfecta cognitio, ideo dicit: cum causam arbitramur cognoscere; quia vero est actualis cognitio per quam scimus simpliciter, addit: et quoniam illius est causa; quia vero est certa cognitio, subdit: et non est contingere aliter se habere.
[Introductions and translations © R.E. Houser]