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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Robert Nozick Interview 1990

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Good question

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Is being “woke” a way to gain status?

Why Evolution Is True

This new piece at the increasingly important site Quillette by two academics with the same name (brother? father and son?), is well worth reading. It’s amusing even if not 100% accurate, but it’s accurate enough to strike home, and to make you rethink what Authoritarian Leftism is all about:

The Winegards’ thesis is not entirely new. The Regressive Left, they say, is in effect a religion with a sacred narrative (victimized groups), a moral doctrine (i.e., the power hierarchy in America needs to be reversed) and a priestly caste, which, they say, comprises white intellectuals who promulgate Purity Doctrine as a way of separating themselves from the “hoi polloi” and gaining status. Since status is a zero-sum game—the more others get, the less you have—the “woke” priests spend their time signaling their purity, denigrating others who make missteps, and never engaging in actually effecting change.

We all know people who…

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Readers’ wildlife photographs (and videos)

Why Evolution Is True

There’s a small road just north of Moss Landing, California that runs beside a small estuary that’s terrifically rich in wildlife: birds, otters, sea lions, and so on. It’s been called “The Serengeti of the Pacific”, and we spent quite a bit of time there. Here are some photographs of what you can see.

A long-billed curlew (Numenius americanus), which makes its living by probing sand and mud for crabs and other invertebrates.

Fluffing its feathers:

A long-billed curlew foraging on the beach:

Three sanderlings (Calidris alba). As ecologist Bruce Lyon wrote me, “These are arctic (tundra) breeders and they have an interesting mating system if I recall correctly. The breed as pairs but the female lays two clutches, one that she incubates and one that her mate incubates.”

Here’s a sanderling foraging on the beach. It’s hard to take photos and videos of these birds…

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Best Argument Ever Against Political Correctness by Stephen Fry

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A flipped blue iceberg

Why Evolution Is True

After years of following leads and contacting travel/expedition companies, it looks as if I’ll be lecturing next year on some cruises to Antarctica and the Falkland Islands, which has always been a great dream of mine. It will be great fun lecturing on cruises again (I’ve done it four times), as the audiences are always much more receptive and interested than are the students in a regular college course. And I can’t wait to see the scenery and, especially, the wildlife. And maybe a blue iceberg!

Until I read this article from MyModernMet, and followed the links, I had no idea that icebergs could actually be blue. (They can also be green.) After all, they’re made of water, and water is clear and ice cubes are clear. But this doesn’t appear to be the case with ‘bergs. As the “Met” link reports:

While on an expedition in Antarctica, interface designer…

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Readers’ wildlife photos

Why Evolution Is True

Reader Tom Carrolan sent some lovely raptor photos. Look and learn! (His comments are indented.)

Before Earth Day (1970) and wetland protection laws, the Red-shouldered Hawk (Buteo lineatus) was being extripated from most of Northeastern North America. As various endangered and threatened state laws came into place, this species was added as Threatened. Nesting in wetland forests brought about those listings. In Massachusetts, many of the first strip and enclosed malls were built after destroying Atlantic Whitecedar Swamps along the Route 128 corridor: prime real estate for the Red-shouldered Hawk. This species has recovered in the Northeast — US and Canada — but not to pre-WWII populations.

In the west, the birds are much more richly colored and marked (Bl.eligans). While in the SE, the birds are quite pale (Bl.extimus).

First we have a hawk in hand at Braddock Bay, north of Rochester NY. This is from my…

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Andrew Sullivan on tribalism

Why Evolution Is True

I’ve watched with approbation as Andrew Sullivan, with whom I’ve often disagreed, seems to have mellowed, becoming at least a centrist instead of a conservative, and remaining mum about his mystifying Catholicism.  Sullivan’s nice new column in New York Magazine, on tribalism, starts with Jon Haidt and Greg Lukianoff’s new book, The Coddling of the American Mind, and then goes into the bitter and acerbic polarization of the American electorate, as exemplified by the fracas around Brett Kavanaugh’s nomination (I still am unable to automatically equate accusations with fact) and the firing of the New York Review of Books editor Ian Buruma simply because he published a piece by an accused sexual assailant (Jian Ghomeshi) who was acquitted. Sometimes I feel the world has gone mad, and I no longer know where I fit in. I can’t align with the extreme Left, whose actions often seem fascistic…

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My letter to the University of Michigan: why a professor can’t refuse to recommend students on the grounds of political disagreement

Why Evolution Is True

As I reported earlier today, John Cheney-Lippold, an associate professor of American Cultural Studies at the University of Michigan refused to write a letter of recommendation for an undergraduate to study in Israel—after first agreeing to do so and then finding out it was Israel. Cheney-Lippold subscribes to the anti-Israel Boycott, Sanctions, Divestment movement (BDS) and thus considered withdrawing his offer to write as a demonstration of his personal ideology. In contrast, I considered this a dereliction of duty, not a demonstration of academic freedom. It hurts a student’s career, wishes, and prospects in order to supposedly preserve one’s ideological purity. It is one’s JOB as a faculty member to write letters for students.

I would write for any student that I felt I could support on academic grounds, regardless of where they wanted to study. I would, for example, gladly write a letter for a student to study…

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Michigan professor rescinds offer to write student a letter of recommendation—after he discovers it was for study in Israel

Why Evolution Is True

This is the equivalent of deplatforming a speaker after he or she has been invited to speak. In fact, it’s worse, for it involves impeding a student’s career because of an associate professor’s ideological stand.  The professor is in cultural studies (of course), John Cheney-Lippold in the Department of American Culture at the University of Michigan. And the story is reported in both the Washington Post and the student paper, The Michigan Daily; click on the links below to read (h/t: Rodney).

Washington Post:

The Michigan Daily:

From the report in the Post:

The clashing visions turn on a reference letter, one of the most valuable currencies of the teacher-student relationship. At the University of Michigan, the letter of recommendation is now also a tool in the protest against Israel, as John Cheney-Lippold, a professor of cultural studies, this month rescinded his offer to write on behalf…

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