Astrology and its sceptics

Few subjects split an evening as reliably as astrology. Half the table finds it fascinating, the other half calls it superstition, and most of the time the two sides talk past each other. Here the objections are taken apart calmly, one after another, including the places where the criticism is simply right.

Three objections that have nothing to do with each other

When someone says the whole thing is nonsense, three very different thoughts can lie behind it. They are worth separating, because each one calls for an answer of its own.

• The psychological objection: the texts are worded so broadly that anyone can recognise themselves in them.
• The empirical objection: under controlled conditions astrologers are right no more often than chance alone would lead one to expect.
• The physical objection: no force is known through which a distant planet could shape a person.

The first aims at the wording, the second at the procedure, the third at the grounds. Anyone who packs all three into one sentence ends up arguing about nothing in particular.

The Barnum effect and what you can do with it yourself

The psychological objection is the strongest. Specialists know the mechanism as the Barnum or Forer effect: if the same deliberately general description of character is put in front of a group, with the claim that it was drawn up for each of them personally, most of them find it strikingly accurate. A sentence such as “on the outside you come across as sure of yourself, on the inside you doubt more often than others suspect” fits almost anyone, because it offers both possibilities at once.

On top of that comes confirmation bias. Hits stick, misses drop out of memory. Anyone who reads forty weekly horoscopes remembers the three that fitted.

Two tests against it take ten minutes. First: read the weekly texts for all twelve signs without looking at the headings, and then try to work out which one is yours. Second: write a prediction with its date on a slip of paper, put it away and fetch it out again three months later. Both are sobering, and they are still the only fair way to form an opinion.

A newspaper column and a birth chart are two different things

Much of the criticism hits the section in the weekly magazine, and there it hits home: twelve short paragraphs are handed out to an entire population, sorted by nothing but the month of birth. A calculated birth chart works differently. It needs a date, a time and a place, and it delivers no message for the week but a drawing of the sky over a single place in a single minute.

The point is fair, but it is no acquittal. It only shifts the question: what would then have to be testable is the full chart. And that is exactly where it becomes uncomfortable.

What the tests have shown so far

In the best known experimental designs, experienced astrologers had to match birth charts to the right personality profiles or life histories, without knowing the people. Across many rounds the results did not sit reliably above what plain guesswork would have produced. Individual studies with striking clusters were much quoted, but stayed disputed and could not be repeated reliably.

The argument from forces does not carry far either. The gravitational pull that a distant planet exerts on a newborn, once it is worked out, comes to far less than the attraction of the people standing in the same room. Experienced astrologers therefore hardly ever appeal to physical influences, but to a correspondence between the state of the sky and the event, that is, to a simultaneous pattern. That is more honest, but it leaves the matter without scientific grounds: a correspondence can be asserted, it cannot be measured.

What is left when all of that is subtracted

None of it adds up to a proof, and anyone who promises you one is selling you something. What is left is a system of order: twelve signs, a handful of celestial bodies, twelve areas of life. A vocabulary for traits that everyday life has no words for, and an occasion to talk about things that otherwise go unspoken. No study decides whether that is worth anything to you; you do.

Two attitudes help here, whichever side you are on: take nothing on trust that you cannot check for yourself, and distrust anyone who uses the sky to frighten you or takes money to avert a misfortune he has foretold. Anyone who wants to form an impression of their own will find a level-headed way in at the free horoscopes and in the overview of astrology.