In the previous post, I gave a brief overview of the history of knowledge (otherwise known as epistemology) and argued that humanity has slowly given up essential tools to assessing reality. During the section devoted to ancient realists, I mentioned the three laws of logic as they pertained to how realists viewed the world. In this post I would like to go a little further with these laws by providing definitions as well as some practical examples of how they work.
These laws, originally presented in Aristotle’s Posterior Analytics, are as follows:
The Law of Identity
Definition: A is identical to itself and different from other things.
This idea may seem too commonsensical for anyone to bother postulating it as a formal law of logic, but do not discount its simplicity. Being aware of the Law of Identity can actually save your life. Imagine waking up in the morning and stumbling into your bathroom where you open up your medicine cabinet and see two bottles of pills in tablet form. One says “Tylenol” and the other says “Arsenic”. The Law of Identity states that Tylenol is Tylenol and cannot be anything other than Tylenol. The same is true for the bottle of arsenic. So we could say, then, that a person is not justified in swallowing a couple of tablets of arsenic while pretending that it is identical to Tylenol. As an aside, the Law of Identity really becomes useful when figuring out whether the mind and the brain are identical. For my thoughts on that issue, click here.
The Law of Noncontradiction
Definition: A cannot be both true and false in the same sense at the same time.
If I were to tell you that my car was a black Camaro, it would be impossible for my car to be a black Camaro and not be a black Camaro at the same time. Pretty simple, right? This law is helpful in discussions about the nature of truth. For example, when disagreeing with others some people like to say, “What’s true for you is not true for me.” Unless the conversation is about something subjective (like favorite ice cream flavor) the Law of Noncontradiction reveals that statement to be incoherent. For example, if I were to tell you that the entire world we experience is an illusion (which is a typical Hindu belief), then the world cannot both be an illusion and not an illusion at the same time. Likewise, if I were to tell you that there is no such thing as a supernatural aspect to reality (which is a typical materialist/Atheistic belief), then my statement could not be true on Wednesday and false on Sunday. It is either all true or all false.
The Law of Excluded Middle
Definition: A is either true or false.
This idea seems to be a repeat of the Law of Noncontradiction. But, while the two laws entail each other, they are not the same. Remember, the Law of Noncontradiction states that an idea cannot be both true and false at the same time. Well, the Law of Excluded Middle simply states that there is no third option for an idea being true or false. So, for example, if I had a belief that the tablets I just swallowed were Tylenol, then it is only either true or false that the tablets are actually Tylenol. There is no third option between true and false.
How does this apply to, well, everything we do? Take your experiences driving a car as an example. How do you know that the car keys in your pocket belong to your car? The Law of Identity. Your car keys cannot be identical to any other set of keys except itself. So you get in your car and drive on the street. Why should you not drive on the left side of the road (in America)? The Law of Noncontradiction and Excluded Middle. If you decide to drive on the left side of the road, cars will quickly speed towards you. It would be impossible for these cars to be speeding towards you and not speeding towards you at the same time. It is also impossible for there to be any other option than the cars’ either speeding towards you or not speeding towards you. If, somehow, you were brave enough to disregard the laws of logic, what do you think would happen next?
Reality. Would. Seriously. Harm. You.
This is only one of many examples of how we use the three laws of logic regularly (whether we are aware of it or not). They are so embedded into every aspect of our existence that, if these laws somehow went away, reality would be nothing more than incoherence and randomness. Therefore, beware the worldviews that can neither give a proper accounting for these laws nor affirm their value/necessity.
 I have used updated language consistent with Aristotle’s definition in Posterior Analytics.