I began this series began by discussing logic, because good thinking – critical thinking – is a skill one must develop, much like learning to play piano. Learning logic is to the thinker what learning chords and finger placement is to the pianist. Critical thinking can be arduous, for the topics and issues to which critical thinking must be applied are oftentimes the same topics and issues that make us the most emotional; moreover, we are forced to find balance between two seemingly opposing inclinations, as Carl Sagan explains:
“It seems to me what is called for is an exquisite balance between two conflicting needs: the most skeptical scrutiny of all hypotheses that are served up to us and at the same time a great openness to new ideas … If you are only skeptical, then no new ideas make it through to you … On the other hand, if you are open to the point of gullibility and have not an ounce of skeptical sense in you, then you cannot distinguish the useful ideas from the worthless ones.” [1]
As we continue on in this series, I must note that, even though it may be important, the path of a critical thinker is often a difficult road. Maybe that’s why most people don’t bother to attempt it, and choose instead to remain with their comfortable and familiar beliefs.
The Path of a Critical Thinker
• Inductive vs. Deductive
Two types of arguments — inductive and deductive — are distinguished this way: a deductive argument is one in which, if the argument is sound, it’s impossible for the conclusion to be false, whereas an inductive argument is one in which, if the argument is sound, it’s merely improbable for the conclusion to be false.
Put another way: a deductive argument deals with certainly, whereas an inductive argument deals with probability. Consider again the Socrates syllogism:
Premise 1: All men are mortal.
Premise 2: Socrates is a man.
Conclusion: Socrates is mortal.
This is a deductive argument because, if the argument is sound — i.e., the argument is valid (has proper form) and all the premises are true — then the conclusion must be true, and it’s impossible for the conclusion to be false. Now here is an example of an inductive argument:
P1: Sith Lords have only ever used red-bladed lightsabers.
P2: Benedict is a Sith Lord.
∴ Benedict uses a red-bladed lightsaber.
This argument is inductive because, if the argument is sound, then the conclusion is only probably or even most likely true. After all, Benedict might decide to break tradition and start using an orange lightsaber. But probably not.
The level of probability won’t be the same with each argument. The argument that “the sun has risen each day for as long as the earth has been orbiting the sun; therefore, the sun will rise again tomorrow morning,” is much more likely than the argument that “Mr. Jones has gone on his morning walk at 6 AM every day for the past 20 years; therefore, Mr. Jones will go on his walk tomorrow morning.”
Sometimes, what seems to be inductive reasoning may end up being fallacious. For example, if I flip a coin and it lands “heads” nine times in a row, I could argue that the coin will land on heads again because that’s how it has landed each time in the past. This is poor reasoning because there is no apparent causal connection between the previous coin flips. If I flipped the coin 50 times and it landed heads each time, the inductive argument would start to make more sense, and I would begin to suspect that something aside from chance was causing the coin to land the same way each time.
There is also the abductive argument, which starts with a set of observations then seeks to find the simplest and most likely explanation. Abductive conclusions are attempts to show what is most likely the case based on the observations made, and are most often understood as “inference to the best explanation.”
• The Necessity of Logic
Some people deny the value of logic due to either miseducation or misunderstanding of the discipline. A person might argue that “logic is bunk,” but as soon as they try to explain why logic is bunk, they are appealing to the rules of logic. Logic can’t be denied or argued against without using logic and assuming the rules of logic are applicable.
Likewise, one cannot prove that logic is “logical” without using logic to prove it, thus leading to circular reasoning (we will discuss this in more depth when we get to the section on logical fallacies). Some use this argument in an attempt to dismiss logic. They’re right, by the way: we can’t argue for the use of logic without appealing to the rules of logic when we craft our argument.
Still, though we cannot justify using logic without appealing to logic (leading to circular reasoning, which is also part of the rules of logic), the presumption of logic is necessary for us to understand anything at all. If we deny the rules of logic, then we must admit that statements like “God exists” and “God doesn’t exist” are both true statements… and they are both false statements. “The earth is round” and “the earth is flat” are both true and both false. “You are reading this article” and “you are not reading this article.” It doesn’t make sense.
Without logic, there can be no actual communication, and no conveyance of truth. Logic, then, is the most foundational assumption one can make.
Dead-Logic 