Monthly Archives: January 2014

Argument from consequences

The Argument from Consequences, also known as (‘Appeal to Consequences’) or argumentum ad consequentiam [1], is a fallacious argument that concludes that a belief is either true or false based on whether the belief leads to desirable or undesirable consequences.  Such arguments are closely related to the fallacies of appeal to emotion and wishful thinking.  They generally have one of two forms:

Positive form

Premise 1: If P, then Q will occur.

Premise 2: Q is desirable.

Conclusion: Therefore, P is true.


  • Humans must be able to travel faster than light, because that will be necessary for interstellar space travel.
  • I believe in an afterlife, because I want to exist forever.

Negative form

Premise 1: If P, then Q will occur.

Premise 2: Q is undesirable.

Conclusion: Therefore, P is false.


  • Free will must exist: if it didn’t, we would all be machines.” (This is also a false dilemma.)
  • Evolution must be false: if it were true then human beings would be no better than animals.
  • God must exist; if He did not, then people would have no reason to be good and life would have no meaning.

Such arguments are invalid because the conclusion does not logically follow from the premises.  The desirability of a consequence does not make a conclusion true; nor does the undesirability of a consequence make a conclusion false.  Moreover, in categorizing consequences as either desirable or undesirable, such arguments inherently contain subjective points of view.

There are two types of cogent argument with which this fallacy is easily confused:

  1. When an argument is about a proposition, it is reasonable to assess the truth-value (whether it is true or false) of any logical consequences of the proposition.  Logical consequences should not be confused with causal consequences; and truth or falsity should not be confused with goodness or badness.
  2. When an argument concerns a policy or plan of action—instead of a proposition—then it is reasonable to consider the consequences of acting on it, because policies and plans are good or bad rather than true or false.


[1] Latin for ‘argument to the consequences’

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How many triangles solution

The correct answer is 13 triangles – the large outer triangle, plus 9 small inner triangles, plus 3 medium size triangles comprised of 3 triangles each.

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Appeal to tradition

by Tim Harding

Appeal to Tradition or argumentum ad antiquitatem (also known as ‘appeal to common practice’) is a common informal fallacy that occurs when it is assumed that something is better or correct simply because it is older, traditional, or ‘has always been done.’  For example, arguments of this type often begin with phrases like ‘It has been a long-standing tradition that…’ on the assumption that such words are persuasive.

The placebo industry (aka ‘alternative medicine’) relies heavily on this fallacy by appealing to the notion that ‘traditional medicine’ or some rare berry or plant root has been used for thousands of years, often in a hidden valley in some exotic Eastern country.  Strangely, this argument is regarded by the placebo industry (and gullible consumers) as more persuasive than any evidence that the product actually works.  This fallacy is often comitted in combination with the Appeal to Nature fallacy.

This sort of reasoning has the following form:

Premise: P has always been done.

Conclusion: Therefore P is right or good.

This argument is fallacious because the conclusion does not logically follow from the premise.  There are plenty of counterexamples where something that has always been done or believed in is now regarded as wrong or false such as:

  • Belief in the pseudoscience of astrology is thousands of years old;
  • People believed that Sun revolved around the Earth (rather than vice versa) until only a few hundred years ago;
  • The idea of the Flat Earth is much older than the idea that the Earth is round;
  • Slavery was considered normal until only a couple of hundred years ago;
  • Women have continuously been treated like second class citizens in certain parts of the world.

The opposite of an appeal to tradition is an appeal to novelty – claiming something is good because it is new.  This type of advertising hook is often used to sell new technology, such as software updates, when many of us know of new operating systems that have actually been inferior to their previous versions.

Since false beliefs tend to be rooted out over time, the long-term persistence of a belief can provide some degree of inductive evidence for its credibility, but not sufficient to qualify as a cogent argument. There are lots of ancient ideas that have persisted to modern times, but they are still false e.g. astrology, quackery, beliefs in the paranormal etc. 

An appeal to common practice can be valid if the cost of abandoning the practice or switching to an alternative outweighs the benefits of doing so. For example, re-defining the direction of the flow of current in electrical circuits to match the direction of the flow of electrons might aid education by reducing confusion, but doing so would come with the significant cost of re-writing text books and translating any technical material that covered the topic.  Another example is that the cost of changing the calendar to a year zero other than the birth of Jesus would be far greater than the benefits.  Non-Christians would be wiser to stick with the familiar Christian calendar dates.

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Murder mystery solution

Culprit               Weapon           Location
Mrs Red          spanner              kitchen
Dr Purple          rope                     study
Major Yellow     lead piping    library
Miss Beige            gun                   conservatory

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Snail racing puzzle solution

# Owner   Wore  Colour
1 Alfred       3     red
2 Alice         2     green
3 Arthur      4     blue
4 Anne         1     yellow

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Murder mystery puzzle

During a recent murder mystery weekend, four games were played.

In one game Mrs Red used the spanner, but not in the library.

In another game the rope was used in the study, but not by Major Yellow.

During one game the gun was used in the conservatory, whilst in another game Dr Purple was not to be found in the library.

Major Yellow was never in the conservatory and Miss Beige never used the rope.

The lead piping may or may not have been used in the kitchen.

Can you determine who used what and where?

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Classical music puzzle solution

Composer        Format     Length
Beethoven      LP album        6
Holst                      single           7
Bach                        CD               8
Butler                     iPod            9

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Snail racing puzzle

After a recent snail racing contest, the four contestants were congratulating each other. Only one snail wore the same number as the position it finished in. Alfred’s snail wasn’t painted yellow nor blue, and the snail who wore 3, which was painted red, beat the snail who came in third. Arthur’s snail beat Anne’s snail, whereas Alice’s snail beat the snail who wore 1. The snail painted green, Alice’s, came second and the snail painted blue wore number 4. Anne’s snail wore number 1.

Can you work out who’s snail finished where, its number and the colour it was painted?

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Musical Recital Solution

1 = John played Mozart on the Violin
2 = Nick played Bach on the Piano
3 = Kate played Mozart on the Violin
4 = Mary played Bach on the Violin
5 = Larry played Vivaldi on the Piano

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Classical music puzzle

In my collection of classical music I have a range of pieces which last 6, 7, 8 and 9 minutes.

The piece by Bach lasts 8 minutes and the CD lasts longer than the piece by Holst. The piece on my iPod  is longer than the piece by Beethoven. The record single lasts for 7 minutes and the LP album does not contain any Holst. The piece by Butler is on the iPod.

Can you determine which piece of music is on which format and how long each lasts?

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