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 2200 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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I am Ashurbanipal king of the world, king of Assyria @ the British Museum

Books & Boots


Ashurbanipal was ruler of the Assyrian Empire from 669 to about 630 BC. From his capital at Nineveh on the edge of present-day city of Mosul in northern Iraq, Ashurbanipal ruled a vast and diverse empire, reaching from upper Egypt, via the eastern shore of the Mediterranean (modern Cyprus, Israel Lebanon and Syria) and along a corridor either side of the Tigris and Euphrates rivers down to the Persian Gulf. During his reign he was probably the most powerful person on earth.

This blockbuster exhibition examines the life and times and cultural achievements and social context of Ashurbanipal’s rule alongside detailed profiles of the different kingdoms and cultures which he ruled over and exhaustive accounts of his numerous military campaigns.


The quickest way to give you a sense of the scope might be to list some of the headings which introduce different areas of the exhibition and displays:

  • Nineveh, a…

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Whack-a-mole: Knocking the “mobile phones cause cancer” claim on the head

Simon Chapman AO


The first mobile phone in Australia was switched on in 1987. Since then, their use has grown to become almost universal among teenagers and adults for 15 years. There are millions of Australians who have used the phones many times daily since the mid 1990s (24 years). WiFi has been spreading massively in Australia since 2002 (17 years).  If I look at the WiFi neighbourhood networks visible to my home computer, there are 13. If you do the same in a Hong Kong hotel room, pages and pages of network addresses point to a EMR bath you are living in.

If mobile phones really caused brain cancer, today we are in a very good position to test that hypothesis because of the massive numbers who have been exposed, the duration of that exposure and the very high reliability of the outcome endpoint: brain cancer incidence.

If you are diagnosed with any…

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The Gillette Ad redux

Why Evolution Is True

About a week ago when I was in Hawaii, Grania put up a post, “Storm in a jockstrap“, about the new Gillette Razor ad calling out male behavior. This is what Grania said before presenting a bunch of tweets both extolling and opposing the ad.

Gillette has unleashed its latest commercial. Instead of its usual claim that it’s the best a man can get, this time they have opted for some social education and encouraged men to call out other men they see behaving badly. It’s not the worst advice ever given, although I suspect that many in the world are weary of being lectured to, especially by multi-billion dollar corporations; and even more are sick of the call-out culture of social media that may have started in an honest attempt to draw the line against society’s most egregious offenders, but has given way to nasty dog-piling on…

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How to read authors of earlier times who expressed views or created characters that we find repugnant today

Why Evolution Is True

There has been a lot of debate about how—or whether—to read authors whose views (or language) may not comport with today’s mores. Morality evolves, usually for the better, leaving older books bearing attitudes or characters that we find repugnant.

The usual result is to either denigrate or ban these books, and such opprobrium has involved works like Huckleberry Finn, To Kill a Mockingbird, The Great Gatsby, Slaughterhouse-Five, and even The Color Purple. I’m not even mentioning the many books that are deemed verboten by various religions, such as The Satanic Verses. Go to the American Library Association’s Frequently Challenged Books webpage for a comprehensive list.

How do we deal with these books? Do we remove them from libraries, as Confederate statues are removed from campuses? Do we cease teaching them in classrooms—something that’s now happening with To Kill a Mockingbird? Or do we just decry them as…

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Asiatic honeybees make “The Wave” to deter predators

Hiw do they organise the ‘wave’?

Why Evolution Is True

Reader Mehul called my attention to a phenomenon of which I was unaware. It’s amazing too: a “wave” of honeybees in a colony, created to divert or scare away predators. One honey-sipping moth makes it through the bee cloud, but that’s because of another evolutionary trick.

Have a look at this stunning Attenborough segment.

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More about sexual selection in the New York Times

Why Evolution Is True

With the publication of his book The Evolution of Beauty (subtitle: How Darwin’s Forgotten Theory of Mate Choice Shapes the Animal World—and Us), Yale ornithologist Richard Prum gained an extraordinary amount of publicity in the popular press.  His theme was that “beauty”—that is, the evolution of extreme and stunning displays and ornamentation in male birds—results from a form of “runaway sexual selection” in which females’ random preference for extreme male traits produces amazing sexual dimorphism that has nothing to do with natural selection. (The peacock is perhaps the most famous example.) Prum’s book got two separate reviews in the New York Times, at least one other notice, and two big reportorial pieces, including recent the one below. The book was also nominated for a Pulitzer Prize for nonfiction, though it didn’t win.

Prum’s book is worth reading for two reasons. First, it presents a strong defense of the…

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The Madonnas of Leningrad, by Debra Dean

ANZ LitLovers LitBlog

The Madonnas of Leningrad was another impulse loan from the library: the title struck me as incongruous (Religious iconography/Soviet name for St Petersburg), so although the blurb on the back was just the sort of generic praise you expect from an American ‘national bestseller’ I was intrigued enough to read the inside blurb:

Bit by bit, the ravages of age are eroding Marina’s grip on the everyday. And while the elderly Russian woman cannot hold on to fresh memories—the details of her grown children’s lives, the approaching wedding of her grandchild—her distant past is preserved: vivid images that rise unbidden of her youth in war-torn Leningrad.

In the fall of 1941, the German army approached the outskirts of Leningrad, signalling the beginning of what would become a long and torturous siege. During the ensuing months, the city’s inhabitants would brave starvation and the bitter cold, all while fending off the…

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January 21, 2019 · 1:12 am

Democratic National Committee ends its sponsorship of Women’s March

Why Evolution Is True

This announcement, which as of this moment I’ve found almost solely on right-wing websites (you won’t see it in the New York Times or PuffHo), is a serious blow to the Women’s March, since they’ve lost an arm of the Democratic Party, almost certainly because of the antisemitism of the women’s March leaders. This report is from Haaretz, the most left-wing of the venues reporting this:

I won’t belabor this report, as there doesn’t seem to have been any announcement by the Democratic National Committee (DNC) or any explanation, either. The lost sponsorship appears to have been found simply from the DNC’s absence on the Women’s March list of sponsors. As Haaretz (explains

When the list of sponsors for the 2019 national Women’s March was published over the weekend, it became apparent that numerous organizations who had joined the March in its first two years, including the Southern Poverty…

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A computer scientist finds the question of free will uninteresting for bad reasons

Why Evolution Is True

UPDATE: Scott Aaronson has emailed me and pointed out that his views on this matter are set out in a clearer and longer way in a publicly available paper he wrote called “The ghost in the quantum Turing machine.”  It’s 85 pages long, I wasn’t aware of its existence, and it is probably above my pay grade, but perhaps not for some readers who are physics-savvy and also willing to read the paper. If you do, weigh in below. Please consider this post a response to Aaronson’s 8.5-minute explication of free will on the “Closer to Truth” interview and not to the totality of his published views.

I’ll add, with Scott’s permission, a clarification that he emailed me along with the link to his paper:

“Briefly, you can make any theory “deterministic” by the addition of hidden variables, which is exactly what de Broglie and Bohm did…

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The Book Thieves, by Anders Rydell

ANZ LitLovers LitBlog

The Book Thieves was an impulse loan from the library.  I’d heard a lot about the Nazi theft of artworks and their burning of books, but I knew nothing about the systematic theft of books…

But it takes only a moment’s thought to realise that of course there would have been precious collections of books all over Europe, and of course they would have been looted by the Germans, just as the precious artworks and other collectibles were.  Invaders have always looted the possessions of the vanquished, and all the major museums of the world have treasures that originally belonged elsewhere.  In some cases, perversely, that’s turned out to be a good thing: many of Afghanistan’s ancient treasures were smuggled out of the destructive hands of the Taliban and even if they’re in the hands of private collectors now, at least they still exist.  OTOH in the case of…

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