Commonsense and Logic : a concise theory

Here is a long-standing phenomenon (problem, perhaps) in Commonsense Reasoning – commonsense v/s logic. While interpreting any data, there are a lot of possible ways to do it in. These possibilities are logical possibilities. But in everyday life, commonsense takes over, and makes us choose the “commonsensical” possibility. For example, if someone says to you (say, over the phone) – …the pages of the book were moving to and fro..” you would immediately take the meaning to be that the pages were being automatically flipped (within the framework of the book). There is another logical possibility that the book was moving to and fro along the desk, which would also technically amount to “the pages moving to and fro (along the desk)”. Now the questions is – does this possibility occur to the mind and is rejected/discarded or it doesn’t cross your mind even for a second? To a sentence like ‘Mary and Sue are mothers’, Douglas Lenat once mentioned in a talk at Google that “ wouldnt cross your mind even for a second that they are each others’ mothers’ (as in ‘Mary and Sue are sisters’.) I agree with that view. But we are logical beings too. So why dont we take the logical possibilities to this utterance and thereby first enlist the above possible cases and then decide which one to choose? What explains this “not even crossing the mind even for a second”? Below, I provide a concise theoretical explanation for the same.

Given any data, there are 2 ways in which we try to “consume” it i.e. understand. One is a memory-based approach and the other is a logical approach. The first one is predominant in everyday situations (and corresponds to our commonsense). In a memory-based approach you try to relate whatever that is coming at you to your own past experiences – simple – and try to understand it accordingly. In a logical approach you try to take all possible logical cases and deal with the situation. So when you hear about the pages of the book over the phone, you immediately resort to memory to cognize it. You recall situations in your past experience in which pages of a book have “moved to and fro” or/and have also been described in that way corresponding to a certain reality, and immediately arrive at the commonsensical possibility as explained above. This explains how you interpret the meaning without the other logical possibilities crossing your mind even for a second. This explains the immediacy. 

To see this distinction between the two approaches broadly and in general, consider this example. Suppose someone tells you, in everyday life, “the bell rang when we were having dinner”. One immediate response would be “damn frustrating / disturbing!”. Here you have related the data that came at you, to your personal memory and given a response which clearly reflects that. A scientist might have said something overly technical like “was it in the midst of the dinner, or had you just begun, or were about to finish?”
In everyday life we resort to memory-match, as against logical formulation. 

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