When I was growing up my mother often pleaded with me to use common sense. She was evidently convinced I did not have it or else, for some obstinate reason, refused to use it. Perhaps she was right. I was a wool-gatherer, a day-dreamer, off someplace that she did not know or understand. On the other hand, my older brother was evidently a paragon of common sense. I figured this out because she never urged him to use it. He must have been endowed with a suitable supply, for he was an operator and got things done.

The phrase, "Thomas, why don’t you use a little common sense?" still rings in my ear. What is common sense? I have spent much energy and thought on the question; but, the subject is not simple and direct. It is slippery and elusive. What seems to be common sense at first glance is …