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Monday, November 21, 2011

0200: Kant and Aquinas on Non-Contradiction

Entry 0200: Kant and Aquinas on Non-Contradiction

Immanuel Kant (1724-1804) does not deny the principle of non-contradiction. Kant, however, postulated that our knowledge of the principle of non-contradiction is a priori knowledge.

Albert L. Blackwell endorses Kant’s position in the following terms:
Kant is searching for a rational basis for natural science and moral philosophy, and he is correct in asserting that one must begin with the principle of non-contradiction as an a priori assumption. [1]

Aquinas’ position is different. For Aquinas (1225-1274), the human intellect, before it exercises its functions, is tamquam tabula rasa. The intellect, before it has access to the truth, is always “like a clean tablet on which nothing is written.” [2]

And with respect to the first principles in particular Aquinas expressly affirms that “it is from the sensible things of nature that we receive the knowledge of the first principles.” [3] Aquinas often accentuates that there is no access to these principles except through the sensible faculties in direct contact with the sensible things of nature. [4]

Aquinas grants that “the sensible faculties enjoy a certain superiority in regard to the capacity of acting on the intellect and causing knowledge. And this is due to their greater proximity to the exterior things of nature which are the cause and measure of our knowledge.” [5]

Aquinas is unyielding in this point as is seen, for example, when he reasons as follows: “the very habit of first principles is derived from the sensible things of nature, and thus, this habit is the effect of the agent intellect whose function is to act on the phantasm.” [6]

Kant does not postulate the existence of innate knowledge in the human intellect, but only a priori forms.

But the fact that we are able to reach external reality through the intellectual conception of it does not justify the conclusion that thoughts and intellectual conceptions were present in our minds prior to our interaction with reality.

Our knowledge of the principle of non-contradiction is a knowledge caused by the sensible things of nature.


[1] Albert L. Blackwell, Schleiermacher’s Early Philosophy of Life: Determinism, Freedom, and Phantasy, Harvard Theological Studies, no. 33 (Chico, California: Scholars Press, 1982) p. 48.

[2] ST.1.79.2: “Intellectus autem humanus in principio est sicut tabula rasa in qua nihil est scriptum, ut Philosophus dicit in III De Anima.” Also: “Intellectus noster comparatur tabulae in qua nihil est scriptum;” De Ver.8.9. “Anima enim, secundum se considerata, est in potentia ad intelligibilia cognoscenda: est enim sicut tabula in qua nihil est scriptum;” ST.3.9.1.

[3] Q. disp. De anima,4,ad 6: “Cognitio enim principiorum a sensiblilibus accipitur.” Also: “Sed ipsorum principiorum cognitio in nobis ex sensibilibus causatur;” SCG.2.83.

[4]Cognitio principiorum accipitur a sensu;” In Boet. De 4. “Cognitio principiorum provenit nobis ex sensu;” ST.1-2.51.1. “Sic igitur intellectus humanus habet aliquam formam, scilicet ipsum intelligibile lumen, quod est de se sufficiens ad quaedam intelligibilia cognoscenda: ad ea scilicet in quorum notitiam per sensibilia possumus devenire;” ST.1-2.109.1. “Oportet quod in intellectu nostro sint quaedam quae intellectus noster naturaliter cognoscit, scilicet prima principia, quamvis etiam ista cognitio in nobis non determinetur nisi per acceptionem a sensibus;” De Ver.8.15. “Quamvis intellectu sit superior sensu, accipit tamen aliquo modo a sensu, et eius objects prima et principalia in sensibilibus fundantur;” 1. “In nobis perfectum iudicium intellectus habetur per conversionem ad sensibilia, quae sunt prima nostrae cognitions principia;” ST.2-2.73.3. “Primorum autem principiorum cognitio a sensibus (ex sensibilibus) ortum habet;” De Ver.10.13. "Prima autem principia scientiarum speculativarum sunt per sensum accepta;” ST.1-2.3.6.

[5] De 3: “Vel dicendum, quod inferiores vires quantum ad aliqud superiores sunt, maxime in virtute agendi et causandi, ex hoc ipso quod sunt propinquiores rebus exterioribus, quae sunt causa et mensura cognitionis nostrae.” Also: “Illa quae habent deficiens esse, secundum hoc deficiunt a cognoscibilitate intellectus nostri, quod deficiunt a ratione agendi;” 12.

[6] SCG.2.78.n. 7: “Nec tamen intelligendum est quod intellectus agens sit habitus per modum quo habitus est in secunda specie qualitatis, secundum quod quidam dixerunt intellectum agentem esse habitum principiorum. Quia ille habitus principiorum est acceptus a sensibilibus (II Posteriorum) et sic oportet quod sit effectus intellectus agentis, cuius est phantasmata, quae sunt intellecta in potentia, facere intellecta in actu.”