Anniversaries of space exploration

Armstrong, Collins & Aldrin - Photo NASA

Fifty years after the arrival of man on the Moon, a couple of European sexagenarians remember the first landing:

“Do you know what day is today?”

“Saturday, why?”

“I mean the date.”

“July 20th 2019, what about it?”

“Exactly fifty years ago, man reached the Moon.”

“Oh yeah! But wait, there is something wrong here, didn’t they arrive on the twenty-first?”

"No, it was the twentieth, but it took them over six hours to get down from the capsule. By then, in Europe it was the twenty-first, but in the United States it was still the twentieth.”

“True! I remember it well. I saw it on TV. I was ten years old.”

“Me too.”

The fallacy of life on Mars

Mars image mosaic from the Viking 1 orbiter

In a previous post I discussed the fallacy of the invisible cat, where the cause was the confusion between a sufficient and a necessary condition, as indicated by the following table:

Correct deduction: Necessary condition	Fallacious deduction: Sufficient condition
B is true only if A is true. B is true. Therefore A is true.	B is true if A is true. B is true. Therefore A is true.

There is another very similar fallacy, which also consists of confusing necessary and sufficient conditions, but in reverse. In this case, the right and wrong syllogisms are indicated by the following table:

Correct deduction: Sufficient condition	Fallacious deduction: Necessary condition
B is true if A is true. A is true. Therefore B is true.	B is true only if A is true. A is true. Therefore B is true.

Let us look at one example of this fallacy, applicable to the existence of life in Mars:

Water is necessary for the existence of life.

There is water on Mars.

Therefore there is life on Mars.