Sunday, August 2, 2009

Common Sense and Logic vs. Facts

One of the blogs I read, whose writer I disagree with emphatically on the topic of firearms, has written a post in which he makes the following statement:
This is where common sense and logic come in, attributes which are sometimes lost in the pursuit of "facts" and "proof."
The interesting part of the statement above is that the writer seems to be the embodiment of the exact opposite.

He has repeatedly taken a stand of more and more gun control or regulation. In spite of the fact that posters have provided evidence (proof, statistics, etc.) that are completely contrary to his philosophy, he continues to hold to his views what little acknowledgment of the facts that have been presented is usually countered by the point that logic and common sense have to play a role.

So for today's post, let me explore what role logic and common sense have in decision making. Everyone make thousands of decisions daily. And for each of these we rely on a certain amount of logic, facts, and morals. Logic should tell us what the outcome of our decision will be, while morals tell us whether that outcome is good or bad.

Logic is a method of thinking. In the strictest sense, a mathmetical proof, uses a defined set of rules to travel from point A to point B. All of the hard sciences recognize their own set of logic rules (many of which overlap with other sciences), and many of the soft sciences have realized the need to have a set of rules to play by.

Logic can be faulty. One can commit any number of logical fallacies (appeal to authority, circular reasoning, etc.) when one is trying to prove a point. People trained to use logic are always on the lookout for these in their own and others arguments. Logical fallacies indicate one has not critically examined his position or made an error in conclusion.

Common sense is a sum of our experience and knowledge. The common sense that everyone has is different - because all of our experiences and knowledge are different. In that sense, common sense is not common at all (except to say we all have something different that we call the same thing). We may say that not running out into the middle of the street is common sense. But would a child know that? So if we further constrain ourselves and say among adults in America, it is common sense to not run across a busy highway.

Does this hold as universal? Probably, I would bet that if you took 1000 adults in America and asked them 98% would say yes. One of the defining attributes of common sense is that one need not think about it, it is a gut reaction. So the next question one should ask is, is it right?

Let's look at the statement logically. "It is not safe to run across a busy highway." Well, we would have to define some terms: safe, run, busy, and highway. Let me confine highway to roads without a permanent set of stops (i.e. interstates, state highways, etc.). Some roads are called a highway but are covered with stoplights and stop signs. Safe I'll define as not getting hit by a vehicle. Run will be a pace equivalent to being chased by a dog (not a rabid dog, just a dog). So far do you see any problems in my definitions? Some may say yes, and I would agree, but for any logical argument you need to have a rigidly defined set of rules, so by agreeing to analyze the statement based on the rules I have set, we can judge the conclusion against those.

The last term is busy. For my purposes I am going to assume that busy is traffic near downtown Los Angeles during rush hour. So, the statement now becomes "Will I get hit while being chased by a dog, if I go across Interstate 5 in Los Angeles, CA at 5:30pm on a Wednesday?" Same statement as before, I have just constrained it with the definitions. My answer when looking and thinking about this critically, "Probably not." Having driven on I-5 in LA at 5:30 pm this year, I know that the traffic has 30 sec bouts of 5 mph - 20 mph with stops of up to 3 minutes in between - hence the term "stop and go traffic." I feel very confident in my abilities to weave and dodge around cars that are stopped or maybe going as fast as I am. My only concern would be the motorcycles traveling in between lanes at 30 mph constantly.

So from this example, we have common sense that tells us one thing, but once we put some thought in to the situation, we find that our common sense could be wrong. Mao Tse Deng knew nothing about agriculture, but ordered the countries farmers to plant the rice plants only half the distance apart (thereby doubling the amount of rice). No other factors changes - no added fertilizer, not a new breed of rice, just the distance between plants. The result was an unmitigated disaster. The worst rice crop ever and 20 million people died of starvation in China as a result. Common sense decisions are the worst, when we have no background to develop the "common sense" in the first place.

Facts are simply that. Facts. They don't have a political agenda, they don't care about you, they are completely emotionless. People may interpret facts different ways, but any logical interpretation will have to take into account all of the facts. If new facts are brought forth that discount the previous interpretation, then the interpretation must be changed (otherwise you are delving into the realm of faith). For instance, if I look at data of airplane hijackings during the 70s, 80s, and 90s, and find that rarely did everyone on the flight lose their lives; I could then logically conclude that if a plane is hijacked, the best method of dealing with it is to cooperate with the hijackers and let the authorities on the ground handle the situation (this worked dozens of times). After 9/11, one would be a fool to think that this interpretation was still valid. Which may be the reason the few instances of hijacking since then have been met with passenger resistance.

This process of interpreting the world based on facts and changing that interpretation when new facts are presented is also known as the scientific method. Common sense can be used to deal effectively with small problems that have limited amounts of data input if we have the proper prior information (i.e. touching a hot stove will get you burned). If we dealt with complex problems using only common sense, we would never have such things as evolution, quantum mechanics, calculus, and organic chemistry. These concepts are not common sense. The people who developed them didn't just happen upon them one day while taking the dog for a walk.

So if common sense is not common and sometimes makes no sense, what good is common sense for decision making? Well, it should be the first step to formulating a hypothesis. (Common sense is right many times, although not always for the reason we think). This should then be backed up by factual information. If the facts are contrary to common sense, then the common sense was wrong. This doesn't mean you are stupid, only that you didn't have sufficient information and experience. Logic dictates how you frame the argument. It has nothing to do with whether the argument is correct. Faulty logic only means your proof is invalid, it does not mean that the result is incorrect.

In closing, facts are integral to any kind of proof. They validate whether a hypothesis (or common sense) is correct or not. Logic provides the framework for your argument. Appealing to common sense or logic because the facts don't support your case indicates that argument doesn't have a leg to stand on.


  1. Great post. It really talks to the heart of the gun control issue.

    "Common Sense" might say "less guns = less deaths" but the reality is just the opposite because the crooks are already getting as many guns as they want, so the "good guys" will the ones buying 'more guns'. Common sense doesn't always explain things.

    Heck, common sense said that the earth stood still and the sun moved around it, right?

  2. As usual, Reputo, you do an outstanding job isolating, explaining, and then destroying the problem... Sadly, the person who should read this the most will not understand it.

  3. I read your post and then read this one

    and couldn't help be see the parallel. One person's own research still conflicts with their logic and 'common sense'.