But, everything that has four legs. Is not a cat....

All animals have four legs(major premise)

A dog has four legs (minor premise)

Therefore, I ( a dog) is an animal

But to write :

All animals have four legs (major premise)

I have four legs (picture of a dog)

Therefore I am a cat. (obviously incorrect)

The first is an example of a valid syllogism, the second is not.

To repeat my early assertion. I am, therefore I think, because existing comes before you thought upon reflection that you exist. All that nut Descartes did was say the obvious that by thinking he recognized his existence. Well bully for him!

He then went on to say that was the only thing he could be certain of.....

What I had to say was not contradicting what Descartes wrote, but turning it on its head and pointing out something else equally important and more logical, more obvious. He wrote of one thing I wrote of another. My own view is that he should have stuck to mathematics.

I think by this time he stopped speculative mind body dualistic philosophy and concentrated his efforts on Cartesian coordinates-, in x and Y and graphs representing linear and polynomial equations and thereby added to mathematical knowledge.

I probably told this joke before, but here it is again, entitled how to break up with your boyfriend elegantly.

Girl. We're both mathematicians Sheldon (Sheldon is staring mournfully at the tablecloth, eyes downcast).So let me explain it this way.(She waves a piece of paper in front of her, on which is a drawing of the Cartesian co-ordinate system using a parametric equation.Descartes would be proud.)

Let r be the ordinate of our relationship at time t above the point x, where b. Is for boring, o. Is for over it, and m. Is for moving on. .....Are you starting to get any of this Sheldon?

Poor old Sheldon is being dumped....elegantly.