Welcome to Tim Harding’s blog of writings and talks about logic, rationality, philosophy and skepticism. There are also some reblogs of some of Tim’s favourite posts by other writers, plus some of his favourite quotations and videos This blog has a Facebook connection at The Logical Place.

There are over 2100 posts here about all sorts of topics – please have a good look around before leaving.

If you are looking for an article about Skepticism, Science and Scientism published in The Skeptic magazine titled ”A Step Too Far?’, it is available here.

If you are looking for an article about the Birth of Experimental Science published in The Skeptic magazine titled ‘Out of the Dark’, it is available here.

If you are looking for an article about the Dark Ages published in The Skeptic magazine titled ‘In the Dark’, it is available here.

If you are looking for an article about the Traditional Chinese Medicine vs. Endangered Species published in The Skeptic magazine titled ‘Bad Medicine’, it is available here.

If you are looking for an article about the rejection of expertise published in The Skeptic magazine titled ‘Who needs to Know?’, it is available here.

If you are looking for an article about Charles Darwin published in The Skeptic magazine titled ‘Darwin’s Missing Link“, it is available here.

If you are looking for an article about the Astronomical Renaissance published in The Skeptic magazine titled ‘Rebirth of the Universe‘, it is available here.

If you are looking for an article about DNA and GM foods published in The Skeptic magazine titled ‘The Good Oil‘, it is available here.

If you are looking for an article about animal welfare published in The Skeptic magazine titled ‘Creature Features‘, it is available here.

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What is logic?

The word ‘logic‘ is not easy to define, because it has slightly different meanings in various applications ranging from philosophy, to mathematics to computer science. In philosophy, logic’s main concern is with the validity or cogency of arguments. The essential difference between informal logic and formal logic is that informal logic uses natural language, whereas formal logic (also known as symbolic logic) is more complex and uses mathematical symbols to overcome the frequent ambiguity or imprecision of natural language.

So what is an argument? In everyday life, we use the word ‘argument’ to mean a verbal dispute or disagreement (which is actually a clash between two or more arguments put forward by different people). This is not the way this word is usually used in philosophical logic, where arguments are those statements a person makes in the attempt to convince someone of something, or present reasons for accepting a given conclusion. In this sense, an argument consist of statements or propositions, called its premises, from which a conclusion is claimed to follow (in the case of a deductive argument) or be inferred (in the case of an inductive argument). Deductive conclusions usually begin with a word like ‘therefore’, ‘thus’, ‘so’ or ‘it follows that’.

A good argument is one that has two virtues: good form and all true premises. Arguments can be either deductiveinductive  or abductive. A deductive argument with valid form and true premises is said to be sound. An inductive argument based on strong evidence is said to be cogent. The term ‘good argument’ covers all three of these types of arguments.

Deductive arguments

A valid argument is a deductive argument where the conclusion necessarily follows from the premises, because of the logical structure of the argument. That is, if the premises are true, then the conclusion must also be true. Conversely, an invalid argument is one where the conclusion does not logically follow from the premises. However, the validity or invalidity of arguments must be clearly distinguished from the truth or falsity of its premises. It is possible for the conclusion of a valid argument to be true, even though one or more of its premises are false. For example, consider the following argument:

Premise 1: Napoleon was German
Premise 2: All Germans are Europeans
Conclusion: Therefore, Napoleon was European

The conclusion that Napoleon was European is true, even though Premise 1 is false. This argument is valid because of its logical structure, not because its premises and conclusion are all true (which they are not). Even if the premises and conclusion were all true, it wouldn’t necessarily mean that the argument was valid. If an argument has true premises and its form is valid, then its conclusion must be true.

Deductive logic is essentially about consistency. The rules of logic are not arbitrary, like the rules for a game of chess. They exist to avoid internal contradictions within an argument. For example, if we have an argument with the following premises:

Premise 1: Napoleon was either German or French
Premise 2: Napoleon was not German

The conclusion cannot logically be “Therefore, Napoleon was German” because that would directly contradict Premise 2. So the logical conclusion can only be: “Therefore, Napoleon was French”, not because we know that it happens to be true, but because it is the only possible conclusion if both the premises are true. This is admittedly a simple and self-evident example, but similar reasoning applies to more complex arguments where the rules of logic are not so self-evident. In summary, the rules of logic exist because breaking the rules would entail internal contradictions within the argument.

Inductive arguments

An inductive argument is one where the premises seek to supply strong evidence for (not absolute proof of) the truth of the conclusion. While the conclusion of a sound deductive argument is supposed to be certain, the conclusion of a cogent inductive argument is supposed to be probable, based upon the evidence given. An example of an inductive argument is: 

Premise 1: Almost all people are taller than 26 inches
Premise 2: George is a person
Conclusion: Therefore, George is almost certainly taller than 26 inches

Whilst an inductive argument based on strong evidence can be cogent, there is some dispute amongst philosophers as to the reliability of induction as a scientific method. For example, by the problem of induction, no number of confirming observations can verify a universal generalization, such as ‘All swans are white’, yet it is logically possible to falsify it by observing a single black swan.

Abductive arguments

Abduction may be described as an “inference to the best explanation”, and whilst not as reliable as deduction or induction, it can still be a useful form of reasoning. For example, a typical abductive reasoning process used by doctors in diagnosis might be: “this set of symptoms could be caused by illnesses X, Y or Z. If I ask some more questions or conduct some tests I can rule out X and Y, so it must be Z.

Incidentally, the doctor is the one who is doing the abduction here, not the patient. By accepting the doctor’s diagnosis, the patient is using inductive reasoning that the doctor has a sufficiently high probability of being right that it is rational to accept the diagnosis. This is actually an acceptable form of the Argument from Authority (only the deductive form is fallacious).


Hodges, W. (1977) Logic – an introduction to elementary logic (2nd ed. 2001) Penguin, London.
Lemmon, E.J. (1987) Beginning Logic. Hackett Publishing Company, Indianapolis.

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Rationality may be defined as as the quality of being consistent with or using reason, which is further defined as the mental ability to draw inferences or conclusions from premises (the ‘if – then’ connection). The application of reason is known as reasoning; the main categories of which are deductive and inductive reasoning. A deductive argument with valid form and true premises is said to be sound. An inductive argument based on strong evidence is said to be cogent. It is rational to accept the conclusions of arguments that are sound or cogent, unless and until they are effectively refuted.

A fallacy is an error of reasoning resulting in a misconception or false conclusion. A fallacious argument can be deductively invalid or one that has insufficient inductive strength. A deductively invalid argument is one where the conclusion does not logically follow from the premises. That is , the conclusion can be false even if the premises are true. An example of an inductively invalid argument is a conclusion that smoking does not cause cancer based on the anecdotal evidence of only one healthy smoker.

By accident or design, fallacies may exploit emotional triggers in the listener (e.g. appeal to emotion), or take advantage of social relationships between people (e.g. argument from authority). By definition, a belief arising from a logical fallacy is contrary to reason and is therefore irrational, even though a small number of such beliefs might possibly be true by coincidence.

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Readers’ wildlife photos

Why Evolution Is True

I’m BAAACK! Thanks to Grania for filling it with some great Hilis (and other posts) in my absence.

We’re returning to our regular readers’ wildlife feature, and I have a reasonable backlog to tide us over. We’ll begin with some doings on Stephen Barnard’s property in Idaho; winter is coming on and it’s migration season, most notably for MALLARDS (Anas platyrhynchos). Here is his latest batch of photos; Stephen’s notes are indented:

I’ve been trying to capture the phenomenal number of mallards migrating through, but I can’t do it justice. There are several hundred visible in the creek this morning (seen from inside my house through windows). At times there have been several thousand in my 1/2 mile stretch of the creek, or resting and feeding in the barley fields, or flying in vast flocks, in starling-like mumurations, seeming for the joy of it. There’s a lot of…

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Asia Bibi reportedly denied asylum in the UK because of “possible unrest” among “certain sections of the community”

The UK government seems to have its moral principles confused.

Why Evolution Is True

Not long ago I wrote about the plight of Asia Bibi, a Pakistani Christian who was sentenced to death for blasphemy after she got into a row with the Muslim women in her village. As I wrote at the time:

The details of her case show a country steeped in hatred, ignorance, and faith (some of these words might be redundant). The story started in June of 2009 (9 years ago!), when Bibi was bringing water to a group of farm workers in her village. Bibi was a Christian, a mother of four, and then 38 years old. The other workers, who were Muslim, objected to Bibi touching the bowl, and she might even have taken a sip from it.

The details of the altercation then are unclear, but Bibi was accused of insulting the Prophet Muhammad. (As the Supreme Court just ruled, this claim was probably fabricated as…

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How the Animal Kingdom Sleeps

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Is age a social construct?

Why Evolution Is True

Race is now a social construct, gender is a social construct, and even species is a social construct (remember the “otherkins“, who identify as members of a nonhuman species?). Well, this is the logical result, as reported by the Guardian:

And why not? Mr. Rateband feels he’s being discriminated against because of his age and, more important, he feels as if he’s 49. And so he went to court:

A 69-year-old Dutch “positivity guru” who says he does not feel his age has started a battle to make himself legally 20 years younger on the grounds that he is being discriminated against on a dating app.

Emile Ratelband told a court in Arnhem in the Netherlands that he did not feel “comfortable” with his date of birth, and compared his wish to alter it to people who identified as transgender.

Ratelband said that due to having…

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Weigh in on the elections

Why Evolution Is True

I just woke up in Paris to find out that the Democrats have won fairly big in the House, now controlling that chamber, but that the GOP has retained control of the Senate. The governors’ races seem to be a toss-up, with no resolution yet, though I’m not sure why those aren’t as settled as are the Congressional seats.

It is mildly heartening that the Democrats won the House, but that just guarantees a stalemate for two more years, and of course it’s a Republican Senate who would confirm any new Supreme Court appointment, which may be likely if Ruth Bader Ginsburg resigns. Remember, too, that Trump can veto any legislation passed by Congress, and it requires a 67% vote to overturn a Presidential veto.

Given the reportedly big turnout of Dems and groups like Hispanics, this does not bode well for Presidential re-election in two years, which will be…

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The Last Summer, by Boris Pasternak, translated by George Reavey #BookReview

ANZ LitLovers LitBlog

The Last Summer is only 90-odd pages long in my Penguin Modern Classics edition of 1960, but it’s more than a short story.  Titled Povest (A Tale) when first published in 1934, it’s not listed among Boris Pasternak’s works in the Russian edition of Wikipedia, suggesting that perhaps the original was never published in the USSR as a separate title. (As far as I can tell, that is, using Google Translate’s word сказка meaning fairy tale, fable or story).  Maybe Povest was published in a journal or a collection, and only published separately as a book when it was translated in 1959 by George Reavey and published by Peter Owen in the afterglow of Pasternak’s Nobel Prize in 1959.

The first thing to say about the introduction by Pasternak’s sister Lydia Slater is that it’s more about legacy-building than about clarifying the story.  There are a great many superlatives, and…

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The Art of Mesoamerica: From Olmec to Aztec by Mary Ellen Miller (1996)

Books & Boots

Two things about this book:

  1. It is very academic and scholarly. I imagine its main audience is university students. It pays a lot of attention to academic debates about dates and discoveries and conflicting interpretations of the evidence.
  2. This makes you realise it is a fast moving field, with new discoveries being made all the time, and that these discoveries sometimes significantly alter our understanding of timeframes and influences.


Thus the book opens with a daunting chronological table which has six columns, one each for Central Mexico, Oaxaca, Gulf Coast, Maya Highlands, and Lowland Maya – and 10 rows indicating time frames from 1,500 BC onwards.

Chronology of Mesoamerica by Mary Ellen Miller Chronology of Mesoamerica by Mary Ellen Miller

Apparently early archaeologists named artefacts from around 600 AD ‘classic’ and the name, or periodisation, stuck, despite not really fitting with later discoveries, so that successive archaeologists and historians have had to elaborate the schema…

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A Perfect Stone, by S.C. Karakaltsas #BookReview

ANZ LitLovers LitBlog

Greek migrants have been coming to Melbourne ever since the Gold Rush but their numbers surged in the postwar era when Arthur Calwell’s ‘populate or perish’ immigration program offered hope and a home to peoples devastated by the war.  People of Greek heritage are now an integral part of the fabric of our city, so much so that Melbourne is said to be the third largest Greek city in the world. Like many other Melburnians I have friends of Greek heritage and I have celebrated their festivals, dined in their restaurants, and tangled my toes in Zorba’s dance to the music of Mikis Theodorakis on Greek Independence Day.  And yet until I read A Perfect Stone by Melbourne author Sylvia Marakaltsas, I did not know a thing about the Greek Civil War (1946-1949).

Even more embarrassing is that I did not know that amongst the genial older Greeks of my acquaintance…

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Why No Giant Mammals?

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