We look at each other and "demand" that others be reasonable. This is how we know what is true, who is right, what is fair. A conclusion is "valid" only when it passes the test of reasonableness. Whether in marriage, as parents, in business, and especially in the public policy arena, we accept what is reasonable and we reject what is not. That's what we do without much consideration of what we are doing.
Did you know that the criteria of "being reasonable" is at the core of philosophy and is one of the major areas of contention between Martin Luther, the author of the Protestant Reformation, and Thomas Acquinas, the first Catholic philosopher.
The ability to reason was advanced by Plato and Aristotle as the main facility humans had that animals did not. Being able to experience via physical senses multiple data points in the world and inferring a moral principle from this data is innately human. Acquinas believed that by following Aristotle's model of cause and effect we can reason that God exist. Luther took exception. He believed human reasoning could not determine matters of faith. Evidence of God cannot be confirmed through physical senses.
You may not ever think about what it means to be reasonable, but you build your life on being reasonable all the time. You demand it of others. Isn't that interesting? Yet, you may not even understand whether you or anyone else is actually being reasonable. What is reason based on? If you wish, we can explore what it means to be reasonable. You never know what you might find.
What is reason? The 1828 Webster dictionary says reason is the basis by which we reach or justify a determination or conclusion. In this sense, everyone is reasonable in that they have a way to judge or determine what they conclude. However, is everyone's reason really reasonable?
Let's examine this question by breaking the process down to its two components: 1) the starting point and 2) the thought path or logic used to get from the starting point to the conclusion.
There is a field of study for the second component, the logical pathway to conclusion. For instance, there are accepted paths of logic, such as "if A = B and B = C, then A = C." There are aspects of the logic process called fallacies, which is drawing a conclusion that violates laws of logic. You can accept these laws or not, but most scholars of reason would agree on the ways in which logic works. Often, if a thought path adheres to the rules of logic, we would agree the conclusion is reasonable. This is what Aristotle and Acquinas basically do. They apply accepted paths of logic to observations to determine what is true.
So, why did Luther vehemently disagree with Aristotle and Acquinas. Luther pointed to the problem of the starting point. In other words, regardless how logical your path is, if you start at the wrong place, your conclusion will not be reasonable. The starting place for Aristotle and Acquinas was never at question by them. They assumed every human has the same built in core assumptions that make them human. This is what psychology and philosophy has spent thousands of years studying.
Luther claimed that this natural human assumption starting point for reason is flawed. This issue of a flawed starting point is found in the doctrine of Total Depravity of man that came with the fall (Adam and Eve's misstep). Luther believed that humans cannot reason things of God because their logic starts from a place that leads them away from God. Luther believed that revelation not reason is the way man concludes the ways of God. Jesus said that he reveals truth, implying man does not find it on their own from observing the world.
Going back to the meaning of reason, which is simply a pathway to reach a conclusion, I agree with Luther's reason that humans cannot be reasonable. They can be logical but they have a flawed starting point.
However, I have reasoned that humans can be reasonable if the process of thought and emotion follows basic principles of logic applied to an unflawed starting point. My reasoning finds that the starting point is what Luther calls faith. Humans have been given the ability to think and feel about the revealed faith they have received. This is the work of the transformed mind. It seems this is what the historical debate between faith and reason is missing.
Therefore, I encourage you to refrain from trusting reason from the wrong starting point, but also do not reject the idea of reason when it is logic applied to the right starting point.
We claim our judgments are reasonable. We demand that others be reasonable, or we reject their judgments. Being reasonable is not so simple, maybe even impossible for some. Yet, I find it reasonable to ponder, "can you be reasonable?"