05/28/2004: "Logic..."

"This is not logical, it just issss, the same way as Mount Everest isssss, and Elmer Kogan isn't."

Spot the quote? Its from an old Monty Python sketch, from the Soundtrack to "Holy Grail" I think, a little break where a guy rants on about how illogical his wife is.

She deduces "If I buy kippers it will rain", or "You don't love me anymore".

I couldn't find the text of the skit (but I did find some excellent Python sound bites), but it always amused me, and, it made me want to learn more about logic....

(click below for a little rant on logic)

Now logic is more than just being logical... there are some clear mathematical fundamentals behind logic that I was taught many many years ago, but that most people have a slim grasp on. My example? The Atkins diet. So, here goes the logic that I am hearing the masses apply to Atkins:

Given that:
- If I stop eating Carbohydrates, I will lose weight
- If I lose weight, I will be healthier

People deduce:
=> Therefore, if I stop eating carbohydrates, I will be healthier

And as a corollary (and we won't get sucked into an argument on how to pronounce that word)
=> Therefore, if I eat carbohydrates, I will be unhealthier.


WRONG!!!!!

Consider this alternative case:

- If I chop off one of my legs, I will lose weight
- If I lose weight, I will be healthier
=> therefore, if I chop off one of my legs, I will be healthier

Get the idea? OK, the first problem is not exactly one of logic, but of a falacial statement. Losing weight is not necessarily healthy guys! It all depends on how you lose weight.

As for the second one, that is a logic error. Consider this case, an old adage from my army days.

- If you don't eat, you don't shit
- if you don't shit, you die.

=> If you do eat, you don't die.

Well, that would be nice, wouldn't it? Eat your way to immortality!


So anyway, I thought a quick lesson in logic would be useful.

- lesson one - a logical assumption based on a falacial supposition cannot be trusted.

It doesn't mean that the conclusion is wrong, it just doesn't mean for sure that its right. So, before bothering with logic, check your assumptions!

- lesson two - you cannot simply invert a logical statement

You have to be careful with logical inversions. In fact, there are three logical inversions, the inverse, the converse, and the subverse. Honest, go look it up! I can't for the life of me remember which is which, but the trick is, only one of them produces a true result - the others produce falacial results (i.e. neither true nor false).

So, consider the much abused:
- I think, therefore I am.

Inverting this in the three ways, you get:

- I don't think, therefore I am not.
- I am, therefore I think
- I am not, therefore I don't think


Can you spot which of these three is actually true? $1 prize for the personal who correctly labels the inverse, subverse, and converse above. If it helps, try substituting "I'm Spam" for "I think", and "I'm pink" for "I am" (and not the other way around!!!)