R.Hansen says: >The car example didn't meet your satisfaction?
I like the car example! Reversing time is a favorite of mine. I accept all the sensible things that can be said this infamous rule, and even some of the silly.
(What I was questioning was: "repeated subtraction twice, which is back to repeated addition". Lost me there. Strikes me as a sleight-of-speech.)
Going on, I've just been pointing out that this particular issue has a long and colorful history, and in some sense remains a conundrum. Look, people *do* learn the rule. That's not even my point, as if it stops 'em cold.
But just look around the web today - this remains a stumbling block, a puzzler, an enigma to many people. Chalk one of for "formal reasoning" if you like -- people did not establish this rule here by common sense (alone) for sure, but the desire to understand via common sense endures, and is apparently frustrated, at least on an case-by-case basis. Time travel and un-losing poker hands are nice, but they just don't have the force of two apples plus three apples.
Somebody no doubt now, wants to explain it to me in terms perhaps even I can understand. They are not getting my point. Its not what I, you, or they understand about it, or what their niece or grandmother knows, its just the general morass that this infamous rule has created in the past over the general populations and continues to create today. Say what you will, those facts remain.
Now, my own little pet ideas, I've already enunciated: teach negative numbers as composite entities, don't say silly things like "quantities less than nothing", etc. I don't believe that I've somehow cured the common cold now, though, really.