Modus Ponens & Modus Tollens

An arguer wrote, to me, yesterday night, in defense of 3067 BCE proposal as the year of Mahabharata War.

He went on a long diatribe about me, explaining (trying to) me how my logic of AV observation is incorrect and how Professor Achar (or Professor Raghavan) have nailed the precise year of Mahabharata war with one simple observation of ‘planet Saturn near nakshatra Rohini’.

He presented a long discourse on ‘Modus Ponens’.  Of course he could have simply provided me with Wikipedia link, which would have been equally confusing.

Interestingly, he showed complete lack of awareness of ‘Modus Tollens’.

So what is this business of ‘Modus Ponens’ & ‘Modus Tollens’.  I will refer you to wikipedia for extended reading.

In brief….

There are two consistent logical argument constructions: modus ponens (“the way that affirms by affirming”) and modus tollens (“the way that denies by denying”). Here are how they are constructed:

  • Modus Ponens: “If A is true, then B is true. A is true. Therefore, B is true.”
  • Modus Tollens: “If A is true, then B is true. B is not true. Therefore, A is not true.”

There are two related incorrect and inconsist constructions: affirming the consequent and denying the antecedent.

  • Affirming the Consequent: “If A is true, then B is true. B is true. Therefore, A is true.”
  • Denying the Antecedent: “If A is true, then B is true. A is not true. Therefore, B is not true.”

Let’s apply this to claim for 3067 BCE as the year of Mahabharata war.

As many of you are aware that ONLY observation (from the Mahabharata text) that can be claimed to corroborate 3067 BCE as the year of Mahabahrata war is ‘Planet Saturn was ‘afflicting’ nakshatra Rohini’.  Of course this statement can be (and must be) interpreted in the context. However, one can give a small (only very small) benefit of doubt to the proposal for year 3067 BCE by saying that ‘Saturn was indeed near nakshatra Rohini in 3067 BCE)


Our arguer was trying to advocate logic of ‘Modus Ponens’ in an incorrect fashion.

A:  3067 BCE is the year of Mahabharata War

B: Saturn was near nakshatra Rohini during 3067 BCE

Since B is true, therefore A is true.

Why is this incorrect and inconsistent?

This is because claim in ‘B’ was also true for many other years,. e.g. 1971 CE, 2001 CE and in fact any year separated from 3067 BCE by ~29.5 years (orbital period of Saturn) or ~ multiples of 29.5 years.

While logic of ‘Modus Ponens’ is applied in everyday life, one must understand that this is not a logical law and is an extremely weak logic when it comes to evaluating scientific theory ( conjectural followed by empirical and experimental).

Unfortunately, it remains, an entrenched myth, to this day, even in scientific circles, that progress in science came through logic such as this (Modus Ponens).

Revolutionary progress in science has come from falsification of existing theory/proposal rather than piling of additional evidence for an existing theory.  The logic of it can be described via ‘Modus Tollens’

Let’s explore the Mahabharata ‘AV observation’ for the claim of year 3067 BCE, via ‘Modus Tollens’

A: 3067 BCE as the year of Mahabharata War

B: Mahabharata text states that Arundhati was walking ahead of Vasistha at teh time of Mahabharata war.  Arundhati was NOT walking ahead of Vasistha (as demanded by MBH text observation) in 3067 BCE

since B is NOT true, A is NOT true.

Thus claim for 3067 BCE, as the year of Mahabharata War is falsified.





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