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Ontology & Logic
Ontological laws embrace all of reality.
— They apply to everything that exists, not just thought.
Logical laws are laws of thought.
— They are normative. That is, they deal with how we ought to think if we want to reason logically and validly.
The logical laws — also known as the laws of thought — receive their justification and grounding from the ontological laws. The Law of Identity, the Law of Contradiction, and the Law of Excluded Middle are each an “ontological law” and a “logical law.”
These three laws are not matters of subjectivity or psychology.
Each is grounded in reality, in existing things.
From an Aristotelian-Scholastic perspective, being is primary:
— Whatever that is, is.
— Being is and non-being is not.
Ontology is the study of being. It’s about the general truths about being as such. It deals with issues like modality, essence, identity, persistence, causation, substance, etc. Since all that exists is a being, ontology is broader than and deeper than any of the empirical sciences. Philosophy is thus both antecedent to and presupposed by empirical sciences such as physics, chemistry, or biology.
“A being” is simply “that which is.” It is something that has actual existence. “That which is” combines “that which” and “is.” “That which” refers to some subject and “is” refers to its existence. Hence a kind of duality is at the core of ontology: essence and existence. Whatever facts we can arrive at about the various things of our experience, those things need not be. There is thereby a distinction between what they are and that they are.
This is an important distinction in Scholastic ontology.
Perhaps the most basic statement possible is this: “Whatever that is, is.” Next in line is: “Being is and non-being is not.” These statements immediately raise both the Law of Identity and the Law of Contradiction. If we deny these laws, then all intelligibility is destroyed: since being can then be regarded as the same as non-being.
To quote Aristotle: “The same attribute cannot at one and the same time both belong and not belong to the same thing” (Metaphysics, III. c3, s10).
This is not only a law of thought, it is a law of extra-mental reality. Our minds are designed to think, and in that sense aim at understanding being.
Reginald Garrigou-Lagrange, a theologian and philosopher, points out that the Laws of Thought are such “only because they are first laws of being and of reality” (Philosophizing in Faith, p. 269).
The ontological form of the Law of Contradiction proceeds its logical form. The former deals with being as such: a being cannot both be and not be in the same manner and time. The logical form deals with propositions that we can form in our minds: “S is P” and “S is not P” cannot both be true.
Fulton Sheen, a popular Catholic archbishop and Thomist, iterates this point. In the real (or ontological) order a genuine contradiction is “impossible,” while in the logical order it is “inconceivable” (God and Intelligence in Modern Philosophy, pp. 172-3).
Accordingly, we can see why logical laws are normative. That is, “normative” as it concerns what we ought to do. After all, human beings can, and often do, think illogically. The issue is that we shouldn’t! Yet, despite these laws being normative, they have an objective basis in reality, i.e., in being as such.