As You Were

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In the previous post I said that,

*The Principle of Identity*: The dog is a dog.

*The Principle of Non-contradiction*: The dog is a dog, and not anything other than a dog.

*The Principle of Excluded Middle*: It’s either a dog or not a dog.

I regret to inform my readers that I actually got them a little off. I
understand now that I could have said it more accurately this way:

*The Principle of Identity*: The dog is a dog.

*The Principle of Non-contradiction*: The dog cannot be both a dog and a
non-dog at the same time and in the same sense.

*The Principle of Excluded Middle*: It is either true or false that this is
a dog.

These are the three classical principles of logic. Truth is exclusive and absolute. Once we depart from these principles, we cease to make sense. Let’s take the common claim that there is no such thing as absolute truth. Is that claim true? If that claim is true, then it isn’t. Since the statement contradicts itself, it cannot be true. The principles of logic are useful because they help us rule out what is not true.

Let’s examine these principles in greater depth. The principle of identity is fairly obvious. The dog is a dog. We could be wrong to say that it is a dog if it turned out to be a cat, but then per the principle of identity the cat is a cat.

Say that the identity of the animal is in dispute. I say the animal is a
dog, but Jessica says it is a cat. Both of us might be wrong, but if the
animal turns out to be a dog it cannot be a cat, and vice versa. This is
where the principle of non-contradiction would be useful. The animal cannot be a dog and a non-dog at the same time and in the same sense. Norman Geisler explains the principle of non-contraction this way: There are at least two ways to express this principle: (1) it is impossible that contradictory statements be simultaneously true; (2) if one contradiction is true, the other is necessarily false.

-*Should Old Aquinas be Forgotten: Why Many Evangelicals Say No: The Thought of St. Thomas Aquinas Considered*, Chapter 6: The First Principles of Knowledge

Finally, the principle of Excluded Middle can be described as the either/or principle, or the true/false principle. Either the animal is a dog, or it is something else. It is either true of false that the animal is a dog.

I hope this post clears up the muddled explanation of first principles from the previous post.

~Jared

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