Abduction and the no-miracles argument

The Cheshire cat,
famous invisible cat

In an earlier post in this blog, I explained with an example the mode of reasoning based on abduction. Although not as strong as deduction and induction, abduction reaches high degrees of confidence in fields such as history, art criticism and others, less scientific than mathematics or natural science.

In another post published in March 2016, I described the fallacy of the invisible cat, which confuses a sufficient condition with a necessary condition for something to happen. This situation occurs when there are several possible causes that may have given rise to the same phenomenon.

In some cases, if we apply abduction to a situation where the fallacy of the invisible cat could occur, a conclusion can be reached. Think of the example I proposed to describe this fallacy:

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.

The fallacy of the invisible cat

Isaac Newton

In Chapter 1 of his book Astrology, science or belief? published in 1992, Manuel Toharia writes:

However wise they can be about certain subject matters, there is always some element that contradicts the myth of the perfect genius. For example, it is well-known that Newton was an angry man, terribly unfriendly and probably a repressed homosexual. Lest there be any misunderstanding, we must add immediately that what we find wrong with this alleged homosexuality of the English genius is its repression, which certainly made him a bitter person, no doubt with a minimal dose of self-esteem.

Probably a repressed homosexual? And how can we know this, if it is true that Newton repressed it? Or did Toharia (or whoever was his original source) have inside information, or perhaps he came to this conclusion because he knows that Newton suffered at least two psychic crises in his life, and believes that their cause must have been his repressed homosexuality? Observe the use of the qualifiers certainly and no doubt. If so, his argument would be a textbook example of the fallacy of the invisible cat: