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  • Writer's pictureRobert Currey

Twelve logical fallacies every astrologer should know.

"There are two ways to be fooled: one is to believe what isn't true, the other is to refuse to believe what is true." ~ (Kierkegaard 1847)

Sooner or later anyone who has studied astrology will be pulled into a heated debate. Like sex, death, religion, Trump and Brexit, astrology is a controversial topic. What is strange is that those who dismiss astrology outright, know nothing about it and have a false notion of what it is. Here's my equation - [b = 1/k] bias (b) against astrology is inversely proportional to knowledge (k)!

In any debate, trying to 'win the argument' or to humiliate or to convert the sceptic is counter productive and futile. It should be more of an education than a discussion. All that is required is to corral the critic through the logical steps to a point where there is only one rational way ahead: suspend judgement of astrology until the subject has been studied, the claims known and the evidence checked.

It's a two-way process. The more an astrology student debates astrology, the more he or she can reflect on what it is. Claims can be scaled down to a justifiable size. And helping people to understand the rationale behind astrology improves the public image of astrology to the benefit of everyone.

The preamble to any discussion will probably start with a bit of popular myth about “predicting fortunes by the stars”. At this point it is important to set up a definition of astrology.

If a sceptical critic is merely following feelings, then that is a personal belief. This is 'scientism' and as with any a religious fanatic, it is better to agree to disagree. But if the critic is claiming that astrology is false on a scientific or logical basis, then the burden of proof has shifted onto the claimant and they should state their case. Then once the false assumptions and logical fallacies are 'exorcised', the only tenable scientific position is one of healthy doubt or agnosticism until proved otherwise.

The top 12 logical fallacies to avoid and to identify:

1. Appeal to popularity (argumentum ad populum) assumes that an idea or proposition is true because many people believe that it’s true.

  • “Astrology has to be true. Look how astrology features in so many magazines around the world.”

  • But equally “Astrology has to be false because the scientific consensus is that it’s not valid.”

Most scientists are not interested in astrology and have no deep thoughts about the field. Criticism comes from the fringe of science.

Many people believe that lightning doesn’t strike the same place twice. Nevertheless, popularity does make this belief true. Lightning hits the Empire State Building in New York about 20 times per year.

2. Appeal to tradition or appeal to antiquity (argumentum ad antiquitam) claims that an idea that has been around for a long time is true simply because it has stood the test of time.

  • “Astrology must be valid as it has survived for over four thousand years.” Again, so has belief in a variety of bizarre gods, creationism and a flat Earth.

3. Appeal to novelty (argumentum ad novitatem) asserts that that an idea is correct or superior, simply because it is new and modern. This is the reverse of the Appeal to Tradition fallacy.

  • “How can people still follow a primitive belief such as astrology?”

Ancient wisdom has often been lost, only to be rediscovered centuries later. The Antikythera Mechanism is a two-thousand-year-old analogue computer from ancient Greece.

According to recent research, 3,700 years ago the Babylonians invented a long-hand method of calculating trigonometry that is more precise than those used today (Mansfield 2017). Note, that it was in this same region from around this period that the foundations of astrology were empirically discovered (Currey 2017).

4. Appeal to Authority or Argument from Authority (argumentum ad verecundiam) relies on the opinion of a supposedly reputable source to prop up a claim.

  • Since Professor Cox and deGrasse Tyson assert that astrology is rubbish, it must be false.” It also happens that these opinionated pop science presenters are clueless when it comes to astrology (see Uninformed Opinion). Unfortunately, the Press tend to confuse astronomers with astrologers and give them undue weight.

But this fallacy is applied both ways:-

  • “Astrology preoccupied many of the greatest polymaths in history, Ptolemy, Al Buruni, Copernicus, Dee, Cardamo, Galileo, Kepler, Napier, Goethe, Ramanujan, Jung and the greatest novelists Chaucer, Shakespeare, and Rowling.” This means that astrology should be taken seriously, but it doesn’t make it true. Besides, more recent discoveries could have invalidated their views. (see Appeal to Tradition)

5. Argument from ignorance or appeal to ignorance (argumentum ad ignorantiam) assumes that a lack of proof is sufficient to make a claim true or false.

  • Since there is no proof that Pluto impacts life on Earth, it’s impossible.”

Or the counter argument ...

  • Absence of evidence is not evidence of absence” is only viable if you’re refuting an unsupported claim.

Neither statement can be a basis to make a claim about astrology. The burden of proof is always on the claimant whether pro or anti-astrology. In a rational debate, any claim must be supported by empirical evidence. Otherwise it remains a belief.

6. Uninformed Opinion or Argument by Laziness occurs when the arguer hasn't bothered to research the topic, but nevertheless has an opinion. Wikipedia is based on secondary or tertiary sources and is often manipulated. Fact check primary sources wherever possible.

  • "Astrology is rubbish!" or "Astrology flies in the face of four centuries of evidence, from Galileo to the latest space probe." (Jones 2011) or "....that's all rubbish, right, astrology, because the planets are in different places at different times." (O’Briain 2011)

7. Proof by Assertion happens when someone declares a "fact" without supporting evidence.

  • “Astrology violates the laws of science!” Which laws?

  • “Tests of astrology have shown it to be false!”

Obviously, an infinite number of tests would be needed to prove a negative. But even if the claim is based on a few tests, I have yet to see a single test that is not fatally flawed that supports this claim. The claimant must “put up or shut up” as skeptical magician, Randi would say. But here we looking at astrology scientifically so that tests that are based on Sun Signs alone or a single astrologer or a magic trick don’t count. A quick search will confirm that any tests cited are either flawed in obvious ways or after review are shown to support astrology.

  • But then, astrologers claim “Astrology works!” This is fine for describing the astrologer/client subjective experience, but it does not make our claims objectively valid. A placebo works and is now an accepted tool in medicine. But to show that astrology also works on an objective level, assertion and anecdote cut no ice. Statistical evidence is required to show that it works outside the astrologer/client consulting room.

8. False equivalence is to compare two different situations or views as if they are the same.

  • Astrology is like Racism” (Radford 2011). Some people use astrology to label people as stereotypes based on their signs, when the signs are archetypes and few people conform exactly to type. While this false assumption can lead to well-intended minor misunderstandings, it is not equivalent to racial prejudice and the resulting discrimination. There was no holocaust or slavery based on zodiac signs. It is wholly inappropriate, not to say distasteful and disrespectful to all, to make this comparison. This example is also an appeal to emotion fallacy, where emotion is used in place of reason to manipulate the argument. A fair equivalence would be to compare astrology with studies of blood group types.

9. A straw man argument misrepresents an opponent's position. This is done by replacing the opposing argument with a corrupted version. It is then easy to ridicule this much weaker argument and create the illusion of refuting the original position.

  • “The constellations of the zodiac have moved and so the zodiac is out of alignment and astrologers are in error.” This old hoax has been pushed by people who know better.

Having criticised astrology for years, Richard Dawkins, only attacked the soft target of Sun-Sign astrology when given the opportunity by Channel 4 (UK) (Dawkins 2003).

10. Psychogenic (or Psychogenetic) Fallacy is debunking an idea based on its origin and the motivations of the proponent rather than addressing the substance of the argument. This includes ‘Argumentum ad hominem’ which is to attack an opponent's authority, character or other personal traits to undermine his or her argument.

  • “We can dismiss his evidence as he’s an astrologer. He must be biased as he makes a living from astrology.” Yet, the best evidence can only come from experts in the field.

Any argument or evidence presented by an astrologer or a debunker should be judged on the merits of the case and supporting evidence not on their affiliation or vested interests. Most outspoken critics of astrology or those who attempt to 'disprove astrology' with a test, tend to have their views reinforced through membership of sceptical groups (Skeptical - as they prefer to style themselves). But this fact does not in itself undermine their argument or experiment.

11. Slippery slope or the thin edge of the wedge asserts that a relatively small concession inevitably leads to a significant development that is extreme and unacceptable.

  • If we don’t quash Gauquelin’s evidence of an eminence effect, where do we draw the line? Fairies, Unicorns.” (another example of False Equivalence)

My advice to astrologers and our critics is to be prepared to concede openly and with grave, once you realise that you are wrong on a point. No doctor would defend all doctors or all medical techniques, why should you? Those who cannot admit when they are wrong will dig themselves into a hole defending an indefensible position.

12. Circular argument or Catch 22 is to start with a false claim then use it in reverse as

if to prove it.

  • “Astrology is pseudoscience as it is not published in Scientific Journals. Scientific Journals should not publish articles on astrology as it is a pseudoscience.” In practice, scientific journals refer submissions of papers on astrology to astrological journals who publish both positive and negative articles on astrology.

  • “Astrology could not possibly be the explanation for this effect as astrology is too implausible.”

Mechanism and Evidence: issues worthy of debate

Once all the posturing has finished, only two issues need to be addressed.

The first is how does astrology work in a physical sense? It’s really the job of science to find a mechanism to account for all the evidence. Such a discovery would be a great boost to science especially astronomy which is often criticised for having little relevance to human lives. Frankly I don't know the mechanism, but it is worth reading Percy Seymour's book: The Scientific Proof of Astrology (1997) or understanding the Pauli/Jung model of synchronicity, before venturing a strong opinion either way.

The second valid logical argument is – what, if any, empirical evidence supports astrology? These days there are a growing number of compelling experiments.

As I mentioned earlier, some astrology critics advocate scientism – the belief that only science can render the truth about reality. They sincerely believe that they are defending science and reason. In reality, they are religiously defending their personal beliefs based on prejudice and strong emotions. Most devotees have no respect for the scientific spirit of open enquiry. If their beliefs are challenged, cognitive dissonance ensues and some become abusive and mocking of what they see as heresy. Most are not scientists. Nor are they sceptics in the true meaning of the word.

The irony is that most astrologers came into astrology by questioning conventional wisdom and as such, are the true sceptical enquirers.


Currey, Robert (2017) Organisation for Professional Astrologers, June Solstice pp.29-30

Dawkins, Richard (2007) Enemies of Reason, Part 1. Channel 4, UK. Aired 13 August 2007.

Jones, Steve (2011) A review of Impartiality and Accuracy of the BBC’s coverage of Science. BBC Trust Report

Mansfield, Daniel & Wildberger, Norman (2017) Plimpton 322 is Babylonian exact sexagesimal trigonometry. Historia Mathematica, August 2017

O’Briain, Dara (2011) Stargazing Live. BBC2 TV

Radford, Ben (2011) How astrology is like racism. Radford is deputy editor of the Skeptical Inquirer,

Seymour, Percy (1997) The Scientific Proof of Astrology. A scientific investigation as to how the stars influence human life. Quantum

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