Why are liberals and conservatives hardly ever on the same page? Maybe because of the kind of thinking we get accustomed to doing. We can argue back and forth about particular issues, but there is often no common ground because of the difference in methodology - in how we arrive at a particular position.

There are basically two kinds of reasoning: inductive and deductive.

In inductive reasoning, you collect data and make observations, analyze the data, draw conclusions, then test the conclusions against new data. If the data doesn't jibe with your conclusions, you modify or even discard your conclusions and repeat the process. Inductive reasoning is also referred to as scientific method.

In deductive reasoning, you start with a premise, and then logically, step by step, arrive at the conclusion, like in a geometry proof. It's an abstract process in that no data is involved.

The upside of inductive reasoning is that it's empirical. The downside is that when new data comes in, you may find yourself reversing your position. This happens in science all the time, e.g., margarine was good for you until research woke us up to the danger of trans-fats, and then margarine became bad for you. A politician who does this kind of thing can easily be accused of flip-flopping.

The upside of deductive reasoning is that it can give you a core set of beliefs to follow in any situation. E.g., the novelist-philosopher Ayn Rand began with a premise that man acts in his own rational self-interest, and then she logically developed a complete philosophy of ethics and laissez-faire capitalism as a political economy. The downside to this thinking is that if the premise is wrong, everything developed from that premise will be wrong. And, with no built-in reality check, you may not even realize this.

A couple of examples: If you accept the Bible as true, and the Bible says that homosexuality is a sin, then ergo gay marriage should be illegal, according to deductive thinking. Using inductive thinking, on the other hand, you would look at scientific evidence of brain structure indicating that gender preference is largely determined before birth, so you may conclude that treating it as a sin is punishing someone for something outside his control.

Deductive reasoning: If you believe that Saddam Hussein wishes ill towards America, and is plotting against America, then it's probable he is developing WMDs to use against America and is helping Al Qaeda and other enemies of America. The lack of evidence of any of this is irrelevant to deductive thinking. Facts don't matter. Decisions are made based on belief.

This split is particularly noticeable in economics, and actually has been argued back and forth there for the last 200 years. The Neo-Classical schools say the laws of economics are universal, applicable to any group, any society, in any time period. E.g., free trade is right on principle. The other schools that analyze data first then draw conclusions, don't reach the same conclusion. They might say that free trade works for you when you can undercut everyone else's price, but it doesn't work so well for you when you can't - in at least some cases. (It's way harder to come to an absolute conclusion using empirical data than it is using an abstract theory.)

The deductive-inductive split is not necessarily a conservative-liberal split. But I believe conservatives are drawn towards deduction because they're more religious and it's the thinking that religion uses. I.e., conclusions are based on faith rather than observation. From taking the words of Jesus Christ on faith it becomes only a short hop to start taking the words of armchair economists and news pundits on faith - if it's what you want to believe anyway.

Of course, most people don't do all deductive or all inductive thinking. Most people operate on what I call "deductive reasoning with cheating". When faced with facts that are not in accordance with their conclusions, they feel guilty about just ignoring it, so they look for just those facts that support their position. "Hey, I heard about a gay guy who became straight through prayer, so now my position that all gays can change is justified."

Of course, it's very difficult to stick entirely to inductive reasoning, because it means admitting you've made a mistake. The physicist Max Planck is reported to have said that a scientific theory is only replaced by a better one when the original proponents have died off.

So there you have it. Now, think about your reaction to this article. Will you test this theory against observations, or will you dismiss it outright because it conflicts with your core beliefs?

More on this subject can be found on my blog: http://ibrakefortrees.wordpress.com