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 1700 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 recently 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 recently 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 recently 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 recently 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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Americans often find it hard to distinguish between fact and opinion

Why Evolution Is True

There’s a new Pew survey out that asks a timely question, or rather several timely questions. How often can Americans distinguish between factual statements (that is, statements that can be empirically verified or disproven) and statements of opinion? And does that depend on whether the statements are congenial to their ideology? Does exposure to or trust in the news media help you distinguish between fact and opinion?

You can find a summary of the survey (5,035 adult Americans, 18 or older) by clicking on the screenshot below, and the full pdf is here.

Here are the five statements of fact, five statements of opinion, and there were two “borderline” statement that were mixed: part opinion and part fact. (This last group wasn’t subject to as much analysis as the first two groups.)

And here’s what the respondents were asked; remember, a “factual” statement simply makes a factual assertion—it doesn’t…

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Matthew Cobb and others on BBC: “Do insects feel pain?”

Why Evolution Is True

Have a listen to this 26-minute BBC show (click on screenshot to go to the show, which should be accessible worldwide). It’s the second part of a show about whether it’s moral to kill or hurt insects.

A personal note: I avoid killing insects, or any animal, whenever possible. I may swat a mosquito, but if I see a millipede, an earwig, or anything else in my home or lab, I take it outside and release it. Yes, I killed millions of flies doing genetics research over my career, but I always killed them humanely, first putting them to sleep. (When I was doing undergraduate research on flies at William & Mary, I would take my spare flies to the roof of the biology building and let them go. I was finally caught doing this by my advisor, who chewed me out for polluting the natural gene pool—of the cosmopolitan…

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The Seventh Cross, by Anna Seghers, translated by Margot Bettauer Dembo #BookReview

ANZ LitLovers LitBlog

  A brilliantly written escape novel, written while the Nazis were in power and one of the only depictions of a concentration camp to be seen in the midst of war.  The Seventh Cross was an international bestseller in 1942, but it hasn’t been in print in the UK since.

That blurb is a story in itself, eh?  Anna Seghers was a significant author of novels and short stories in pre-war Germany, but as a Communist of Jewish descent she fled with her husband and children to Mexico.  This novel was published there and it became a movie starring Spencer Tracy in 1944.

At this distance it looks like a woeful movie, disappointing because it fails to capture the nuances of the book.  Yes, The Seventh Cross is an escape novel, but it’s also more than that, it’s a cautionary tale about the dangers of surveillance and the way distrust…

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Gods, Power and Knowledge

Andrea Goldsmith

Throughout human history we humans have created gods to help explain our existence. We look to these deities to give meaning to our circumstances, our actions, our past and future, our blessings and our sufferings. That these gods, with their immortality and their extraordinary powers, are often given human form is an interesting paradox: we create them because they are NOT like us, and yet we domesticate them by giving them our bodies and other human characteristics.

The Greeks set the barre high when it came to numbers of immortals. They had gods for almost all aspects of human existence: love, war, hearth and home, harvest and hunting, wine, fire, message delivery, wisdom, fertility, and much much more. The Egyptians put up a stiff competition, so, too, the Romans. Then came the Jews, and after them the Christians and Muslims who dispensed with all but a single omnipotent being –…

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Vote for the kakapo Lego set

The video is hilarious!

Why Evolution Is True

Kakapos (Strigops habroptila), as you should know by now, are the world’s only flightless parrot, and as such—and being residents of once-predator-free New Zealand—are highly endangered, and have been moved to predator-free islands to try to keep the species going. They are also adorable, as well as being horny. Here is perhaps the most popular video of any parrot: Sirocco, the “spokesparrot” for kakapos.

As Heather Hastie points out in her latest post, there’s a campaign afoot to have Lego create a Kakapo Kit, which will produce moveable bird replicas that look like this:

and this:

I’m pretty sure that if Lego builds this thing, part of the proceeds will be used to save this wonderful bird. They…

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Southern Poverty Law Center apologizes to Maajid Nawaz, pays out a $3.4 million settlement for labeling him an “anti-Muslim extremist”

Why Evolution Is True

We’ve talked before about how the Southern Poverty Law Center (SPLC) has abandoned its historically useful mission, now taking after “hate speech” and including among the purveyors of said speech—on a list of “anti-Muslim extremists”—both Maajid Nawaz and Ayaan Hirsi Ali. Nawaz is a practicing Muslim, and Hirsi Ali a former Muslim and now a Muslim reformer whose latest book lays out a peaceful series of steps (granted, mostly impractical ones, like “getting people to stop taking the Qur’an literally”) to defuse Islamist extremism.

Nawaz threatened to sue the SPLC for labeling him as an anti-Muslim extremist. The SPLC then quietly removed its “field guide to anti-Muslim extremists” from its website, but now they’ve had to do more. Here’s a tweet from Nawaz’s foundation, Quilliam, detailing how the SPLC had to apologize and pay big bucks to settle the issue.

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What Is Intersectionality?

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“Ballooning” crab spiders spin silk parachutes, and take off after testing the wind with their legs

Why Evolution Is True

A new study in PLoS Biology by Moonsung Cho et al. (free pdf here; reference below) uncovers some of the mysteries of how spiders (in this case crab spiders) balloon. “Ballooning” is an amazing form of spider dispersal. The spiders, usually very young ones, climb up on some high spot like a blade of grass or a twig, and then emit long strands of silk from their spinnerets on the abdomen; those strands then catch the wind and carry the spiderlets for long distances—even hundreds of miles.

Why do they do this? There are a number of reasons mentioned by Cho et al. including:

  1. Reducing cannibalism by fellow spiderlings
  2. Reducibg competition for local resources
  3. Dispersing to new and more favorable sites
  4. Searching for mates and food

According to the authors, ballooning spiders have traveled hundreds of kilometers this way, colonizing distant “oceanic” (volcanic) islands, and have even been…

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The Enlightenment of the Greengage Tree, by Shokoofeh Azar, translated by Adrien Kijek #BookReview

ANZ LitLovers LitBlog

This novel is an exciting development in Australian publishing.  The Enlightenment of the Greengage Tree is a novel written by Shokoofeh Azar, an Iranian author now living here in Australia, and translated from the Persian into English for publication by Wild Dingo Press.  The only other novel that I know of that has a similar genesis is Oh Lucky Country by Rosa Cappiello which was written in Italian and then translated for publication by UQP.  And that was way back in 1984.

The timing of the release of The Enlightenment of the Greengage Tree this August is just perfect for #WITmonth too.  #WITmonth is an international reading project which shines a spotlight on women authors who write in languages other than English.  It was started because the percentage of women writers published in translation is absurdly low (about 30%) and I am mildly pleased to report my own stats for this have improved markedly…

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Smoky the Brave, by Damien Lewis, guest post by Amber the Silky Terrier #BookReview

ANZ LitLovers LitBlog

The arrival of Smoky the Brave has prompted a departure in guest reviewing on this site.  Since the book is about the heroism of a Yorkshire Terrier during WW2, it seemed appropriate to invite Amber the Silky Terrier, a most perceptive pooch of my acquaintance and a close cousin to the Yorkie, to comment on the merits of the book… since she comes from the same family of tiny but courageous and indefatigable dogs, who could be better to review this heroic tale?

A brief introduction is in order:

Amber is a three-year-old Australian Silky Terrier who has adopted a human family of bookish tastes. (You can see her in this photo, guarding the household collection of recipe books).  She weighs just on four kilos, and like all Silkies is brave and ferocious, fleeing in panic only at the unmistakeable signs of a forthcoming bath.

(She doesn’t like to be…

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