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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Readers’ wildlife photos

Why Evolution Is True

In the spirit of last week’s Penguin Appreciation Day, we continue with our series on biologist John Avise’s penguin shots from a recent trip to the Antarctic, the Falklands, and South Georgia. And remember, it’s always Penguin Appreciation Day, as almost all species are endangered by global warming and the breakup of ice. John’s notes and IDs are indented.

Rockhopper Penguin (Eudyptes chrysocome), Falkland Islands:

Carrying nesting material:

These penguins had nests interspersed with those of Black-browed Albatrosses (Thalassarche melanophris):

Sitting on two eggs:

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A stunning case of mimicry

Why Evolution Is True

I don’t remember encountering this case of mimicry, but it’s so amazing that, when I became aware of it from a tweet (yes, Twitter has its uses), I decided to give it a post of its own.

First the tweet, sent to me by Matthew. He added, “This is the Iranian viper, as featured in Seven Worlds, One Planet, made by the BBC. Amazing.”

You don’t need to translate the Spanish, though, as the video below tells all. I swear that when I first watched it, I thought there was a real spider crawling on the snake’s back.

The snake…

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Divers give an octopus a new home

Why Evolution Is True

This is incredibly cute: the combination of the kind divers helping a vulnerable little octopus, the way the creature explores the proffered shells with its tiny tentacle, and its final acceptance of a new home. Lovely!

Speaking of new homes, check this one out:

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Readers’ wildlife photos

Why Evolution Is True

Today we feature a couple of photos from the past month or so, all sent by reader Christopher Moss. His captions are indented. The first pictures are of a Mystery Bird.

I’m stumped with this one! Starling sized, thin beak (unlike a grosbeak or finch beak), yellow breast and vent, with a whitish belly. No white lines around the eyes like the yellow breasted chat (and the chat doesn’t have the white edging to the primary wing feathers this one has). The best I can think of is that it might be a female northern oriole, Icterus galbula (aka Baltimore oriole, or Bullock’s oriole for the western race). If it is a northern oriole, it really ought to be in Florida or Mexico by now. But then again, I also have a flock of goldfinches that ought to have gone off to their trailer parks in Florida like good Canadian…

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Coordinated wing-waving in bees

Why Evolution Is True

The tweet at the bottom got me looking for longer videos of this mesmerizing behavior, and I found one (from BBC Earth) on YouTube. The coordinated wing displays are said to deter predators, and I can’t think of any other reason for it, but I wondered if it there really were data showing that it has this effect.  This PLOS One paper, however, shows that the shimmering effect of coordinated wing-waving really does deter wasps from picking honeybees out of the mass on the nest.

Another problem is how the bees manage to synchronize their movements so rapidly. In birds like starlings, which also move and change direction rapidly in similar “waves” during their murmutations, it’s been shown that this movement requires each bird to pay attention to and emulate the movements of six or seven neighboring birds. (Following one neighbor won’t enable such rapid changes.) I’ve put…

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January 16, 1547 – Grand Duke Ivan IV of Muscovy becomes the first Czar of Russia.

European Royal History

January 16, 1547 – Grand Duke Ivan IV of Muscovy becomes the first Czar of Russia, replacing the 264-year-old Grand Duchy of Moscow with the Czardom of Russia.

Ivan IV Vasilyevich (August 25, 1530 – March 28, 1584), commonly known as Ivan the Terrible, or more accurately, “Ivan the Formidable” or “Ivan the Fearsome”, was the Grand Prince of Moscow from 1533 to 1547 and the first Czar of Russia from 1547 to 1584.

Ivan IV was the son of Vasili III Ivanovich Grand Prince of Moscow (1479 – 1533) and and his second wife, Elena Glinskaya, daughter of Prince Vasili Lvovich Glinsky from Grand Duchy of Lithuania and Serb Princess Ana Jakšić, member of the Jakšić family.

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Ivan IV, Czar of all the Russia’s.

When Ivan was three years old, his father died from an abscess and inflammation on his leg that developed into blood poisoning. Ivan was proclaimed the Grand…

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Readers’ wildlife photos

Why Evolution Is True

Today we have the second set of bird photos taken by Joe Dickinson on a recent visit to the Merced National Wildlife Refuge in in the California Central Valley near Los Banos (the first set is here). Joe’s captions are indented.

This great blue heron (Ardea herodias)  looks to me like it has some blood on its beak.  Probably scored a gopher or mouse  recently.

This is a yellowlegs, probably lesser (Tringa flavipes).

A congregation of coots (Fulica americana).  I just decided that that is the appropriate collective term for coots.

This and two following, more sandhill cranes (Antigone canadensis).

This gives an idea of the number of geese (Anser caerulescens and Chen rossii).  To make a decent photo, I had to crop this to about 1/3 of the line.

And more geese all the way down.

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Readers’ wildlife photos

Why Evolution Is True

Today we feature the bird photos of reader and regular contributor Joe Dickinson, whose notes and IDs are indented.

Here is the first of two sets of bird photos from a recent visit to the Merced National Wildlife Refuge over in the California Central Valley near Los Banos.

By far the most plentiful species are mixed flocks of snow geese (Chen caerulescens) and Ross’s geese (Chen rossii). These are almost always in mixed flocks, at least here in Central California at this time of year, and are hard to distinguish unless you can see the heads up close (which was not the case this time).

Based on expected distribution, this almost certainly is a white-faced ibis (Plegadis chihi):

Black-necked stilts (Himantopus mexicanus) are among my favorites—so “elegant” looking.

I’m pretty sure this and the following are red-tailed hawks (Buteo jamaicensis)…

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Bertrand Russell on why the term “agnostic” is for show

Why Evolution Is True

Reader Dom sent me a Bertrand Russell quote from what appears to be a very short essay, “Am I An Atheist Or An Agnostic?” (1947)

As a philosopher, if I were speaking to a purely philosophic audience I should say that I ought to describe myself as an Agnostic, because I do not think that there is a conclusive argument by which one prove that there is not a God. On the other hand, if I am to convey the right impression to the ordinary man in the street I think that I ought to say that I am an Atheist, because, when I say that I cannot prove that there is not a God, I ought to add equally that I cannot prove that there are not the Homeric gods.

None of us would seriously consider the possibility that all the gods of Homer really exist, and yet…

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Steve Pinker clarifies issues about his interview

Why Evolution Is True

In my post yesterday about Steve Pinker’s new interview, I made a few critical remarks about his views on identity politics, though by and large I agreed with him. I was more critical about his views on free will.

As usual, because he’s a friend, I alerted him in advance to the post, and asked him about his views about affirmative action (his interview didn’t say anything about that, but one might get the idea he opposed it), as well as about free will. I didn’t get a response from him until after my post went up, and in that response he gave me permission to post the views he set out in his email (of course I always ask in advance). I overlooked that permission and so didn’t say anything. Now that I see it, I’m posting our exchange for the record. Steve does favor affirmative action, but…

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