Entry 0167: Remarks on the Principle of Non-Contradiction (I)
Remarks on non-contradiction:
“A knower who violates the principle of non-contradiction cannot be said to know.” 
“The [principle] of non-contradiction is presupposed universally in any intelligible content of mind.” 
The principle of non-contradiction “is presupposed by every human being in every cognitive act.
“This principle is true of all possible facts, and its truth is presupposed by every cognitive act, from philosophy to science to balancing one’s check book.
“No matter what there is, it is what it is, and it cannot display contradictory characteristics at the same time and in the same respect.
“This applies to all past experience, all present experience, all future experience—and even to things we will never experience.
“If any truth has claim to both fundamentality and absoluteness, it is this.” 
↑ John R. Bowlin, Contingency and Fortune in Aquinas' Ethics, (Cambridge: Cambridge University Press, 1999), p. 99.
↑ Robert E. Gahringer, “The Foundation of Necessity in Practical Reason,” International Philosophical Quarterly, 1962, vol. 2, no. 1, pp 25-49.
↑ Tibor R. Machan, Objectivity: Recovering Determinate Reality in Philosophy, Science, and Everyday Life, (Burlington, Vermont: Ashgate Publishing Company, 2004), p. 33.