Let’s begin with a quick lesson on the two primary types of reasoning: deductive and inductive.
Deductive reasoning is about starting with premises and following those premises to a conclusion. As long as the premises are true, and the logic is sound, then the conclusion must be true as well. Perhaps the most well-known example of a deductive proof is as follows:
- All men are mortal.
- Socrates is a man.
- Therefore, Socrates is mortal.
As long as premises 1 and 2 are true then 3 is logically true as well. You might have noticed that I started this series with what amounts to a long deductive proof. What sets deductive reasoning apart from inductive reasoning is that the deductive reasoning gives us conclusions which must necessarily be true, while inductive proofs give us conclusions that are only probably true.
Inductive reasoning works by taking certain facts, which we will here call grounds, and from them reasoning to probable conclusions. To better understand this let’s look at a hypothetical process of inductive reasoning. Let’s say I come home expecting to eat some leftover pad Thai that I put in the fridge last night. When I get to the fridge I find that the pad Thai is gone, and that the little blue Tupperware container it was in is now in the dishwasher. These are my grounds: the pad Thai is gone, the container it was in is in the dishwasher. From those grounds I can reason that something disposed of my pad Thai There are other grounds too: I know that animals don’t put containers away, so it must have been a human. I know that the apartment has been locked all day, so it was probably my wife who got rid of the pad Thai. I know that my wife does not typically throw away food that isn’t spoiled, so I can reason that she probably ate the pad Thai. Different grounds will lead to different conclusions: for example, I know that my wife doesn’t like my pad Thai so it seems unlikely that she would have eaten it. From there I might reason that my wife may have had a friend over and she might have offered them the pad Thai, or perhaps it was another family member. Now it is certainly possible that someone else might have eaten the pad Thai, but reason tells me that that is unlikely. Why? Because I have other grounds as well to consider, such as the fact that burglars don’t typically break into houses for the purpose of stealing leftovers, and probably wouldn’t put the container away if they did. From all this I conclude that a friend or family member ate my pad Thai.
To recap, deductive reasoning starts with base principles and comes to a sure conclusion. Inductive reasoning starts with grounds and ends with probable conclusions. Inductive reasoning cannot tell us what certainly is, but only what is probable (in the example above it is certainly possible that the family cat found a way to open the fridge, dispose of the pad Thai, and knock the container into the dishwasher, but it is very improbable that it did so). Most scientific theories come from acts of inductive reasoning, and we use inductive reasoning often in our everyday lives. This is because the premises of a deductive argument are usually up for debate, and can often only be reached by inductive means. Arguably the only deductive argument that begins with premises that aren’t reached through induction is “I think, therefore I am.” With all that in mind we must recognize the importance of inductive reasoning. Without inductive reasoning there is no science, very little philosophy, no industry, no agriculture, and no civilization as we know it.
This is where we run into a conflict with determinism. The conflict is a matter of questioning how inductive reasoning actually works. Take my example above: I would say that I came to the conclusion I did because it was the conclusion best supported by the grounds. However if determinism is true then that is not the reason I came to my conclusion; rather, I came to my conclusion because a series of cause and effect relationships in my brain were determined to result in the answer “a friend or family member ate my pad Thai.” I did not begin with a collection of evidence and reason my way to the conclusion, but was rather compelled to come to that conclusion by the laws of physics. And this undermines my conclusion. After all, one of the way’s we recognize bad reasoning from good is the extent to which we can explain someone’s conclusions with non-rational means. If a millionaire tells me that reducing taxes for the rich is the most rational thing to do, I will naturally be suspicious of his conclusion: after all, he might simply believe so because he’s rich and not because he reasoned it out properly. If a Senator makes a speech claiming that a certain oil pipeline is the most rational answer to our energy problems an opponent might try to invalidate that argument by pointing out that oil companies contributed large amounts of money towards his election. A commenter on this on blog made a similar argument against myself, essentially stating that my arguments couldn’t be trusted because I was a Christian. Now in all three of these examples the arguments made may still be valid: perhaps it is good fiscal policy to reduce taxes on the rich, or to build an oil pipeline. However if someone’s reasoning can be shown to be entirely based on non-rational causes then we can safely dismiss their conclusions.
Now if determinism is true then ultimately everything is based on non-rational cause and effect relationships. Atoms do not reason: they react, and they react in ways that are entirely predictable with sufficient knowledge. If, when I reason, the result is based not on grounds, conclusion, and logic but rather on the outcome of a complicated physical reaction then I have no reason to trust that my conclusions are accurate. If determinism is true then human reasoning has nothing to do with facts and logic and everything to do with the architecture of our brains.
Back in my series on the moral argument I mentioned a mad scientist who experimented with pills that changed people’s moral perceptions. Let’s return to this madman now. He’s just developed a new pill: this one changes the architecture of a subject’s brain so that a chemical reaction will occur that will cause the subject to believe that the moon is made of cheese. Those who take the pill soon come to believe with certainty that the moon is solid mozzarella. They know this to be true based, they believe, on solid reasoning. If you ask one of them they’ll even explain it to you: the moon is white, mozzarella is white, and if it was made of rocks then it would fall out of the sky. You might shake your head. You know that the moon isn’t made of cheese because cheese comes from milk that is tended to carefully by humans, and where in the world would you get enough milk to make the moon, and who would turn that milk into cheese? You feel certain that the moon is not made of cheese because of these grounds, and many others besides. However the mad scientist’s subjects feel just as certain as you about their own conclusion.
Now why do I bring up this crazy hypothesis? Simply to illustrate this point: if determinism is true then our own reasoning processes are exactly as valid as the test subject’s! Both (according to determinism) are the result of a series of cause and effect physical processes. Neither have anything to do with actual induction. The only difference is that the reasoning of the subject was caused primarily by the mad scientist’s pill, while your own reasoning is caused by your genetic makeup, the architecture of your brain, and ultimately the pattern that your atoms are currently in.