Introduction

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 2,300 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).

References:

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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Reasoning

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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Bill Nye screws up when tackling a question about free will

Why Evolution Is True

The wheels fell off the Science Guy juggernaut a long time ago, but Bill Nye still tries to heave the ungainly cart forward, desperately trying to remain relevant. As you know, I haven’t been a fan of his “comeback,” for his attempts to sell science have been ham-handed and embarrassing. (See some of my criticism here.)

Here, in a video made in 2016,  he goes way out of his depth to answer a reader’s question on The Big Stink. I came across this while watching videos about free will by genuinely smart people, and then cringed while I watched this one.

In this video an inquisitive man named Thomas asks Nye whether he, Thomas, has free will, which the inquisitor interprets as libertarian free will: “neural causation”, with an independent ego in control of one’s thoughts and actions. He’s clearly asking about libertarian free will because he sets his…

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Readers’ wildlife photos

Why Evolution Is True

Today’s photos, including a plant and many arthropods, come from regular contributor Tony Eales, who lives in Queensland. His notes are indented:

I’m sending a grab bag of some interesting things I’ve photographed lately.

When I was in Western Australia recently I found this beautiful sundew known as the Red-ink SundewDrosera erythrorhiza. I’m a big fan of carnivorous plants and this was a real beauty.

Another personal favourite is the spiders in the genus Arkys. I hope one day to photograph all of the known Australian species in this genus (around 18 in all) and back in March I got my sixth species, Arkys furcatus.

Another personal goal is to photograph at least one member of each insect order. This weekend I upped my count by two with a member of the Webspinner order Embioptera and a member of the Jumping Bristletail order Archaeognatha

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Byzantium: The Decline and Fall (2) by John Julius Norwich (1995)

Books & Boots

This is a review of the second half of the third volume in Norwich’s weighty and famous three-volume history of the Byzantine Empire, from the founding of Constantinople in 330 to the fall of the same city to the Ottoman Turks in 1453.

The third volume covers the period from the catastrophic Battle of Manzikert of 1071 in which the Byzantine army was massacred by the new power in the Middle East, the Seljuk Turks, through to the final triumph of the Ottoman Turks and the miserable fall of the city.

It is a long, miserable and frequently appalling book to read. It took a big effort to get over the emotional trauma of reading about the sack of Constantinople by the Fourth Crusaders in 1204, so traumatic I devoted a detailed blog post to it.

Byzantium: The Decline and Fall contains so much brutality, cruelty, violence…

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Elephants have awesome olfaction (better than dogs): the pachyderms are the only animals to date that can distinguish different amounts of food by smell alone

Why Evolution Is True

This is another recent paper from PNAS, and I’ll put the link in the screenshot (pdf here), but I’m not going to report on it in detail. Rather, this is an excuse to show a video that demonstrates the paper’s main point: while some animals can distinguish greater from smaller amounts of food using vision, elephants can do it using smell. This appears to be the first example of the use of olfaction in cognitive tasks by an animal.  You might think dogs have a keen sense of smell, but they fail the smell test used in this paper.

The journal Science gives the video below as well as presenting a short popular summary of the paper.

To conduct the research, scientists presented six Asian elephants (Elephas maximus) at an educational sanctuary in Thailand with two opaque, locked buckets containing 11 different ratios of sunflower…

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The sack of Constantinople in 1204

Books & Boots

There was never a greater crime against humanity than the Fourth Crusade. (Sir Steven Runciman, 1954)

Until I read John Julius Norwich’s account of the Fourth Crusade, which ended with the devastating sack of Constantinople in 1204, I hadn’t appreciate what a seismic and unmitigated disaster it was.

Norwich’s account of the Latins’ destruction of the biggest, richest city in the world was so harrowing I was depressed for days and found it difficult to continue reading the book in which he describes it, Byzantium: The Decline and Fall.

Like reading detailed accounts of Hiroshima, I just felt that…. after seeing humanity revealed in such appalling colours, why… why go on with anything?

For me, personally, the reason to go on is to understand better. Not to understand perfectly, which I am confident, or acknowledge, is beyond human wit. But just because perfect understanding is an impossible platonic absolute…

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Byzantium: The Decline and Fall (1) by John Julius Norwich (1995)

Books & Boots

In February 1130 on the banks of the river Pyramus (now the Ceyhan) in Cilicia [the Emir Ghazi, ruler of the Danishmends] destroyed the army of young Bohemund II of Antioch in a total massacre. Bohemund’s head was brought to Ghazi, who had it embalmed and sent it as a gift to the Caliph in Baghdad. (p.72)

Raymond of Poitiers, on 28 June 1149, allowed himself and his army to be surrounded by the forces of the Emire Nur ed-Din. The consequence was a massacre, after which, Raymond’s skull, set in a silver case, was sent by Nur ed-Din as a present to the Caliph in Baghdad. (p.120)

Lots of skulls are cut off and decorated. Lots of imperial pretenders are blinded. Lots of armies are massacres, populations sold into slavery and towns razed to the ground. Yes, it this is the third and final volume in Norwich’s weighty and famous…

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The original anti-vax poster

Why Evolution Is True

James Gillray (1756 or 1757-1815) was an English artist, caricaturist and satirist who has been called “the father of the political cartoon”. (Hogarth is another candidate.) Gillray also seemed to be anti-science, as judging from the cartoon below, which expressed the public fear of Edward Jenner’s smallpox vaccination.

The proud owner of the original cartoon below is my old friend Andrew Berry, a lecturer and advisor at Harvard and spouse of Naomi Pierce, Harvard’s Curator of Lepidoptera. They are kindly putting me up in Cambridge for two days.

As I may have reported earlier, Jenner performed the first smallpox vaccination in the late 18th century, but the practice of inoculation, or variolation, in which matter from a smallpox pustule was injected into people, was practiced much earlier in India, China, and the Ottoman Empire.  (People observed that people who survived smallpox were henceforth immune to further bouts of the disease.)

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Luchita Hurtado: I Live I Die I Will Be Reborn @ the Serpentine Sackler Gallery

Books & Boots

This is a really wonderful exhibition. I thoroughly enjoyed it and had a struggle dragging myself away. And it’s FREE!

Luchita Hurtado has had the most extraordinary life and career. She was born in 1920, in Maiquetía, Venezuela, and is still working and painting, 98 years later! In fact the last section of the exhibition features a dozen or so works from just the past twelve months. But let’s start at the beginning…

The 1940s

Untitled (1949) by Luchita Hurtado © Luchita Hurtado, Private Collection. Photo by Genevieve Hanson

This is Hurtado’s first solo exhibition in a public institution, which seems amazing given the quality of everything on show.

The 95 or so works featured here are arranged in a straightforward chronological order to help the visitor make sense of the astonishing range and variety of styles and approaches to making art which have characterised her career.

Very broadly…

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Appeal to Ignorance

 

by Tim Harding

The scope of the Appeal to Ignorance fallacy (Argumentum ad Ignorantiam in Latin) is more limited than its title would suggest. In the specific context of this fallacy, the word ignorance represents ‘a lack of contrary evidence’ rather than a lack of education or knowledge. The fallacy title was likely coined by the philosopher John Locke in the late 17th century.

In informal logic, this fallacy asserts that a proposition is true because it has not yet been shown to be false, or a proposition is false because it has not yet been shown to be true. This represents a type of false dichotomy, in that it excludes the possibility that there may have been an insufficient investigation to determine whether the proposition is either true or false. In other words, ‘absence of evidence is not evidence of absence.’

In rhetorical debates, appeals to ignorance are sometimes used in an attempt to shift the burden of proof.  A typical example is as follows: ‘In spite of all the talk, not a single flying saucer report has been authenticated. We may assume, therefore, there are no such things as flying saucers.’ An absurd but logically equivalent example is: ‘Although NASA has shown that the surface of the moon is not made of green cheese, it has not conclusively demonstrated that the Moon’s core is not made of it; therefore, the moon’s core is made of green cheese.

This fallacy is a potential trap that empiricists need to be wary of falling into. We cannot prove the non-existence of anything, so the burden of proof lies with those who claim the existence of something, rather than those who doubt it. So, we should always remain open to the possibility of new evidence in support of a claim, even if no such evidence has ever been found.

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Van Gogh and Britain @ Tate Britain

Books & Boots

Before I went I’d read some disparaging reviews of this exhibition – but I found it really interesting, thought-provoking, full of wonderful paintings and prints and drawings, and making all kinds of unexpected connections. And big, much bigger than I expected.

The premise is simple: Vincent van Gogh came to live in England at the age of 20 in 1873, He lived in London for nearly three years, developing an intimate knowledge of the city and a great taste for English literature and painting. The exhibition:

  1. explores all aspects of van Gogh’s stay in London, with ample quotes from his letters to brother Theo raving about numerous aspects of English life and London – and several rooms full of the paintings and prints of contemporary urban life which he adored
  2. then it explores the development of van Gogh’s mature style and the many specific references he made back to themes and…

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