The blog of Dr Glenn Andrew Peoples on Theology, Philosophy, and Social Issues

So you think you’re logical?


Take the logic test, devised by Colin Beckley and friends. The test is HERE.

There are actually two short tests, each out of 15. I got 15 for each one, and since I’m an illogical nutjob (so people in the blogosphere keep telling me) I’m sure you’ll all do much better!

EDIT: As Madeleine reminds me, a hat tip is in order! Thanks Mads. πŸ™‚


Politicians can’t argue, and water is wet


Inspired by actual events


  1. Jonathan

    Ack, got careless at the end: 14/15. Fun though.

  2. David A.

    14/15 (didn’t notice the should/could), then 14/15 in the second one (overlooked the inductive/deductive).

    Not bad, considering my philosophy degree is 30 years old. But once you’re taught logical thinking it never goes away (thank God).

  3. Rob R

    booya! Hundred on the first. Didn’t try the second.

  4. Ron

    15 on the first– so I’ll leave on a high note like Costanza and not take the second.

    Alright that’s it for me! Good night everyone!

  5. Colin

    Can someone convince me that the author is right about q12 on test 2.

    Or alternatively, answer my test question below:

    All shnibleuxes are urgulentrics
    I am a shnibleux
    Therefore I am an urgulentric

    Valid or invalid?

  6. Rob R

    well, you see, β€˜Up’ and β€˜Down’ are used in different senses, therefore an ambiguity is committed.

  7. Rick

    I got #15 wrong and Im still not sure why, even with the explanation… Eh well since I’ve never taken a philosophy class, I would say I did rather well considering πŸ™‚

  8. Test 1 15/15. Test 2 15/15.

    Second test took longer. Found the time travel question a little ambiguous. Never studied philosophy or logic formally, but heavy tertiary in maths and sciences.

    To be honest, it is not always the syllogisms that are hard, it is rephrasing sentences into syllogisms that I find more difficult.

    Rick, #15 is inductive not deductive, thus it could still (theoretically) be proven wrong. Think black swan/ white swan.

    Colin, #12 in wrong because to go up above the ground is semantically different from to be up before, or in front of someone.

  9. What no hat tip?

    28/30 for me missed 1 on each – probably due to doing the test at 1am…

  10. Rick

    @bethyada The conclusion is, “Therefore we can predict that every future examination of water will reveal the same chemical composition.”

    That sounds like theory to me. We can make a lot of predictions based on past experiences. Does it mean that it will always be true.. no not even when out of a million times it has been true.. it’s possible we might find an exception. So a prediction would just be a theory and by the observation it seems that we could indeed predict that every future examination of water would reveal the same. We have no reason to not predict it correct? The conclusion goes along exactly with what you said.. it could still be theoretically proven wrong, but there are no absolutes in the conclusion they put forth either… I could just be blind, heh πŸ™‚

  11. Quite right Mads, hat tip added!

    And I did the test later at night than you πŸ˜›

  12. Rick, the point is that the argument is inductive thus invalid. The test is not asking if the answer is true (or sound) just valid. Several of the other questions are valid but unsound because the premises are false.

    But don’t discount the power of the inductive, it is the power of science; whereas the deductive is the power of mathematics.

  13. Rick

    Ugh ok, maybe ill have to revisit it later to make sense of it πŸ™‚ I got all of the others right, plus all of the 2nd page right, so it seems like I would be able to understand the reasoning behind #15 and what you are saying, but Im having a hard time grasping it πŸ™‚

  14. Question 15.
    a) Water is a molecule composed of two hydrogen atoms and one oxygen atom.
    b) Every observation or examination by microscope has confirmed this.

    Therefore we can predict that every future examination of water will reveal the same chemical composition.

    Same structured argument
    a) Swans are birds with white feathers
    b) Every observation or examination confirmed this.

    Therefore we can predict that every future observation of swans will reveal the same white feathers.

    While we can predict this, it is not bound to be true.

    The question would have clearer if he did not include the word predict, because prediction is indeed reasonable. Though he is intending predict here to mean will indeed be the case.

    It is also difficult in that the meaning of water is now tied up to H2O. If we found something that seems to be water physically, but turned out to have a different structure, we would give it a different name.

  15. Nathan

    bethyada, that’s the exact issue I had with question 15. In the author’s explanation of whether the conclusion is valid or not he says there are doubts about what constitutes water, i.e. premise 1 might be false. But that didn’t stop him saying other arguments were valid, even though premise 1 was false, e.g. All ducks bark.

    It is invalid because ‘predict’ introduces ambiguity – it’s an inconclusive conclusion.

  16. Woland's cat

    100% but I do have a slight quibble with #15 (and with the shoddy wording of 13!).

    It seems to me that water defined as H2O is a little more rigid a definition than “Swans have white feathers”. To me it seems that the question is more along the lines of:
    a. Absolute zero is -273.15Β°C
    b. Every observed temperature has confirmed that there is no temperature higher

    Therefore, we can predict that there will never be a temperature lower than absolute zero.

    I would feel obliged to answer “valid” on the basis of the definition in (a) alone.

    I realise that the conclusion doesn’t necessarily follow from (b) but feel that the definition in (a) alone is enough to draw this conclusion. The same with the initial definition of what water is.

    Or am I wrong here? Does the conclusion have to account for both (a) and (b) or can it be overridden by the strong initial definition?

  17. Number 15 (in test #1) is a pretty reliable inductive line of reasoning.

    However, the test says: “Read the following premises, and then specify whether or not the arguments are deductively valid or invalid.”

    Being deductively valid is not the same as being a good argument. In the case of water, all past observations of water being being X does not logically entail that all future observations will be X. So it’s not deductively valid. It’s still decent inductive reasoning, however, which is why some people slip into calling it valid. It’s not valid, because validity is about logical entailment.

    Be sure to try test #2!

  18. Woland's cat

    Sorry, with the absolute zero example I meant, of course, “no temperature lower”.

    And I’ve just reread Bethyada’s last paragraph. It seems we’re both a bit suspicious about the strength of water=h2o vs swans=white-feathers.

  19. It looks like comments 16 and 17 were being typed at the same time:

    WC, I think question 15 means to say that we have established that all examples of water are H20 by observation.

  20. MaxVel

    15/15 on the first test, 14/15 on the second. Pleased with that result.

    Glen, nice to see your blog so active, and interesting. I’m your visitor from Thailand, BTW.

  21. Woland’s cat, I think #15 would be better to use a different example, I think the use of “predict” makes it slightly ambiguous, and I think the (chemistry) definitional nature of water = H2O adds to the problems with the example. But the conclusion is based on induction, not deduction. This is why I (correctly) marked it invalid in the test, as did you.

    This may be a better phrase of the question:

    a) Water molecules were initially observed to be composed of two hydrogen atoms and one oxygen atom.
    b) Every subsequent observation has confirmed this.

    Therefore every future examination of water will reveal the same chemical composition.

  22. Woland's cat

    Bethyada, I agree.

  23. Kristian Joensen

    I scored 15/15 in the first one and 14/15 in the second one. I am pleased with the result.

  24. Haecceitas

    I got question 15 wrong because:

    Water is a molecule composed of two hydrogen atoms and one oxygen atom.

    On the basis of this alone, we can be confident that any future observation that reveals a different chemical composition will not be an observation of water.

  25. LittleShepherd

    15/15 and 13/15.

    I got 6 wrong because I forgot that no matter how much observational evidence exists, it is still induction. Oops.

    I got 10 wrong, and I disagree with their answer. They simply said they are motivated to procreate, not that the procreation in and of itself is to be the motivation. If the motivation is pleasure, this changes nothing. Pleasure motivates them to procreate. If the motivation of pleasure is to be disallowed, it must be done in the premises, not after the fact. Otherwise they are asking us to go against their own rules to only consider the information given in making our decision.

    I got 14 right, but I actually did take the more literal approach. I again disagree with them that such an approach would render the argument valid. If Billy Bunter had a thin person inside him, that second person would not be Billy Bunter(unless by accident of coincidentally having the same given name, which is not the same thing) but a separate person altogether. To say Billy Bunter is two people in such a situation is to confuse the contents with the container. He is one person with a separate thin person somehow inside.

  26. Richard P

    I only did the first test and got 15 out of 15. However I’m still no sure why, in general, I should be logical. Please help me.

  27. LittleShepherd, they are right that argument 10 is invalid.

    “Motivation” enters the picture out of nowhere in the conclusion. Where did it come from? The correct conclusion is: “Therefore creatures procreate.”

  28. LittleShepherd

    I hadn’t thought about that. My first thought was “if a creature does something, there has to be a motivation, so it’s not entirely out of nowhere,” but . . . I suppose there could be actions done w/o motivation by some creatures. Not that I can think of any off the top of my head, but I don’t discount the possibility.

  29. Yeah, things might be done without a person even intending to do them.

  30. Nothing has happened on this blog for months. I’m getting very bored. Can you post something new please.

  31. Paul Baird

    Bugger, only got 14/15. Too much beer watching the Rugby. Got question 10 wrong – weird.

  32. Bryan

    Sorry for being three years too late, but I’m arguing Test 1 Question 15 with my coworkers. To illustrate my reasoning, I’ve altered the question slightly:

    Question 15.
    a) Water is a molecule composed of two hydrogen atoms and one oxygen atom.
    b) Every observation or examination by microscope has confirmed this. This is irrelevant.
    Therefore we can predict that every future examination of water — a molecule composed of two hydrogen atoms and one oxygen atom — will reveal the same chemical composition.

    This substitution of the definition of water with the later occurrence of the term water is logically equivalent as far as my understanding goes.

    I see this question as similar to this:
    a) The natural number 2 is the only natural number which is greater than 1 and less than 3.
    b) Every past observation has found that the only natural number found between 1 and 3 is 2. (This is just as irrelevant in my opinion as the original b) above)
    Therefore we can predict that every future examination of the natural numbers found between 1 and 3 will find only the natural number 2.

    Why can’t we deduce that this definition of the number 2 will still be true in the future?

  33. “This substitution of the definition of water”

    But it’s not the definition of water. It’s the composition of water. It’s not true as a matter of definition that water is composed of two atoms of hydrogen and one of oxygen. That’s the sort of thing that we learn by discovery. Thousands of years ago when people knew nothing of chemical makeup, they still knew just what water is. It’s that clear wet stuff that tastes like… well, not much. They had a fine concept of water. They just didn’t know what it was made of. We can imagine a substance just like water, but discovering that it’s not made of two atoms of hydrogen and one of oxygen. It’s not an analytic truth that this is what our stuff called “water” is made of. In other words, it is not true by definition. As soon as we know what water is, we don’t know that it is H2O. Otherwise the ancients would have known this, because they knew what water was. It’s a synthetic truth, and something we learn by discovery.

    The number 2 is different, because as soon as you know what people are referring to by the number “two,” you know that it’s the whole number between one and three. That is an analytic truth – it’s true by definition. We don’t need to investigate anything or discover anything to see that this is true.

    So that’s the difference between the two cases.

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