We like to think of reasoning as rational — yet we often represent our arguments as fights between adversaries positioned to determine which can wield the greater strength or force. Why do we use such energetic and aggressive images of weakness, strength, defeat, and victory, of boxing in and breaking down an enemy's defense? Why don't we just use cool, clear, faultless reasoning to prove we are right? The answer is that we rarely need to know that anything is absolutely wrong or right; instead, we only want to choose the best of some alternatives.
Here are two different strategies for deciding whether one group of reasons should be considered stronger than another. The first strategy tries to compare opposing arguments in terms of magnitudes, by analogy to how two physical forces interact:
Strength from Magnitude: When two forces work together, they add to form a single larger force. But when two forces oppose each other directly, their strengths subtract.
Our second strategy is simply to count how many different reasons you can find for choosing each alternative:
Strength from Multitude: The more reasons we can find in favor of a particular decision, the more confidence we can have in it. This is because if some of those reasons turn out to be wrong, other reasons may still remain.
Whichever strategy we use, we tend to speak of the winning argument as the stronger one. But why do we use the same word strong for two such different strategies? It is because we use them both for the same purpose: to reduce the likelihood of failure. It comes out the same in the end, whether we base a decision on a single strong argument — that is, one unlikely to be wrong — or on several weaker arguments, in hopes that they won't fail all at once.
What makes us so prone to formulate our reasoning in terms of conflicting adversaries? It must be partly cultural, but some of it could also be based on inheritance. When we use architectural metaphors that speak of arguments as not supported properly, we could be exploiting structures that evolved within our spatial agencies. Similarly, when we represent our reasoning in terms of battling adversaries, we might be exploiting the use of agencies that first evolved for physical defense.