Evolution affirms the Consequent

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  1. Affirming the Consequent is a logical fallacy that takes a known true statement [if P then Q] and invalidly concludes its converse [if Q then P]:
    1. If Bill Gates owns Fort Knox, then Bill Gates is rich. Bill Gates is rich. Therefore, Bill Gates owns Fort Knox. False!
    2. If an animal is a dog, then it has four legs. My cat has four legs. Therefore, my cat is a dog. False!
    3. If it’s raining, then the streets are wet. The streets are wet. Therefore it’s raining. False! It could be raining or it could be something else. The “therefore” claim is false.
  2. How does ‘Affirming the consequent’ apply to evolution? We have not observed “evolution”. No one has, and no one will, despite the effort (see LTEE). What was observed is Resemblance, the Birth Mechanism, Variability and Adaptability. Neither of these (even combined) can logically be extrapolated to “evolution”, namely the hypothesized transmutation of one type of organism into another. Proofs of “evolution” always take the form: If “evolution” is true, then XYZ is true. XYZ is true. Therefore “evolution” is true. This is a classical Affirming the Consequent logical fallacy.
  3. Let’s see some concrete examples of “proof of evolution” fallacies:
    • If “evolution” is true, some fossils are ancestors of and therefore resemble existing organisms. Fossils resemble one another and existing organisms. Therefore “evolution” is true. This argument fails because there will always be some resemblance between two or more entities (even chairs and cats have four legs in general). Also, a fossil can always be from an unrelated branch of the “tree of life” which circularly presupposes “evolution” anyway.
    • If “evolution” is true, organisms are genetically similar. Organisms are genetically similar. Therefore “evolution” is true. This argument is false because other hypotheses such as common design account for genetic similarities just as well.
    • If “evolution” is true, one might expect common embryology. Similar organisms have similar embryology. Therefore “evolution” is true. This fails because embryology is expected to match genetics and morphology, hence the previous counterargument applies.
    • If “evolution” is true, one might expect vestigial organs. What looks like vestigial organs can be observed. Therefore “evolution” is true. This fails because what if those organs are useful rather that “vestigial”? And why would “evolution” not do away with “vestigial” organs as soon as they become useless? In sum, why can’t these organs have another reason or origin than “evolution”?
    • If “evolution” is true, one expects adaptability such as antibiotic resistance. Antibiotic resistance is observed. Therefore “evolution” is true. This fails because adaptabilities such as antibiotic resistance are compatible with other hypotheses, not just “evolution”. In addition, antibiotic resistance is ubiquitous, limited, reversible, and never observed to result in organism transmutation aka “evolution”.
  4. How can “proofs of evolution” avoid the ‘Affirming the Consequent’ logical fallacy? Direct confirmation of “evolution” is unlikely as shown by the LTEE study. Alternatively, an observation that is true for “evolution” and only for “evolution” might also work. In other words, what’s missing from all the examples above is a true statement of the kind: “only if evolution is true, then XYZ”. Of course, excluding all alternatives to “evolution” is an impossible task therefore, given that Intelligent Design is the main rival, proponents of “evolution” need only add a true statement of the kind: “if Intelligent Design is true, then XYZ is not true” to turn their invalid arguments into valid ones. But even this lower bar cannot be met by “evolution” proponents, thus making all “proofs of evolution” invalid.
  5. Isn’t then all science ‘Affirming the Consequent’? For example, “if Newtonian physics is true, a ball thrown at angle Theta and speed V will land D meters away. The experiment is carried out, and we find that the ball landed distance D away. Therefor physics is true.” No! This is not a fallacy because it meets the “if and only if” requirement and is limited to “everything else equal” cases. Rockets do not disprove this claim because everything else is not equal between them and thrown inactive projectiles. In addition, no one claims a single experiment confirms all Newtonian Mechanics the way “proofs of evolution” are presented. In this case, multiple combinations of Angles and Speed result in the same Distance without violating Newtonian Mechanics because this experiment proves only portions of the theory.

Links:

https://en.wikipedia.org/wiki/Affirming_the_consequent

https://www.amazon.com/Biblical-Wisdom-Literature-Joseph-Koterski/dp/1598035258

http://myxo.css.msu.edu/ecoli/

820 thoughts on “Evolution affirms the Consequent”

  1. dazz: Validity doesn’t depend on the premises being true or unambiguous.
    Soundness does.

    Which of those statements are unsound?

  2. phoodoo: Which of those statements are unsound?

    Soundness and validity are properties of arguments, not premises. This has been explained before.

    Premises can be either true or false. Or maybe unknown. Yours are ambiguous and nonsensical. That doesn’t mean that there’s a problem with logic itself

  4. phoodoo:
    walto,

    Under the argument I proposed, it is not possible to ever determine if my Aunt was a soldier.There can be no resolution.

    Look:

    But that can’t happen in my argument.You can’t ever know the degree of truth of the second statement, because you can’t ever know the truth of the first.It fails the basic definition of what an argument is supposed to accomplish.One person can say its true, and another person can say its not true, and both are right.

    I could just as easily have made the second premise, if birds don’t fly my aunt was not a soldier.

    Then I could make my final premise, some birds fly and some birds don’t fly.

    Are you calling that valid?

    Logic and validity have nothiing to do with knowledge–what we can or can’t know. It’s about the relationship of propositions, whether we know their truth-values or not. I’ll say this one last time: An argument is valid when and only when it’s the case that, if the premises happen to be true, the conclusion HAS GOT TO BE TRUE. It has nothing at all to do either with whether the premises ARE true or whether or not we do or can know anything about the premises.

    The other stuff is important too, of course, but it’s not logic.

  5. KN, to Nonlin:

    But (and this seems to be hard for you) a good inference can have false premises and a false conclusion, and it can even have false premises and a true conclusion. It’s only a bad inference is the premises are true and the conclusion is false.

    It can also be a bad inference when the premises are true and the conclusion is true. Sometimes bad reasoners get lucky.

  6. You can just assume the truth of the premises to determine whether an argument is valid. That doesn’t mean they ARE true. A valid argument means that if the premises WERE true, the conclusion also has to be true.

    There’s nothing else to this. It’s about necessary relationships between truth values, given various (logical) forms of statements.

  7. Guys like Nonlin and phoodoo have trouble abstracting the form of an argument away from its content.

    There’s a correlation between being bad at abstract thinking and being an IDer, and I don’t think it’s a coincidence.

  8. First two lectures of an intro to logic class handles all this. There’s a ton of material available on youtube. People who’ve never taken a class would be well-served holding off on posting on whether this or that is valid until they sat with a lecture for an hour or two.

    Anyhow, i’m not correcting these errors anymore.

  9. keiths,

    I think there’s a fear/reluctance not to fight on every front. So evolution must be illogical as well as under-confirmed, overly-optimistic, equivocal, materialistic, immoral, pseudo-scientific, etc. After all, IDers get accused of all that stuff and more.

    But if you don’t actually know what logic or scientific method ARE, you’re not going to help your case attacking others’ use of them. I think it’s better to pick your fights. Find your strengths and what you really understand to be your opponent’s weak areas rather than firing off shots at your own feet.

    ETA: maybe nobody actually accuses IDers of being materialistic. Prolly should substitute “naive” there.

  10. walto,

    But if you don’t actually know what logic or scientific method ARE, you’re not going to help your case attacking others’ use of them.

    Nonlin and phoodoo don’t seem to know that they don’t know. Dunning-Kruger and all that.

  11. DNA_Jock: Yes, you do. You wish to dispute the truth of the first premise, i.e. “If it doesn’t rain, the streets are not wet”.

    No. You have a reading comprehension problem. The premise I do not “wish to dispute” with this particular OP is “evolution is true”.
    I stated:
    “This particular OP is NOT saying “evolution is false”. Of course “evolution” is false, but for OTHER reasons, not because of this fallacy. This OP is LIMITED to “proofs of evolution are all logical fallacies”. Once again, is this so hard to get?

    Who cares about your little sophistry exercise? And what are you trying to demonstrate with it anyway?

    DNA_Jock: The issue is that premise 1 of your second argument assumes a lot of water cannons.

    Ridiculous. What’s “a lot of water cannons”?!? Wet is wet.

    When will YOU (DNA_Jock) admit that “proofs of evolution” are indeed fallacies? YES or NO (with valid counterarguments)! Time is running out. No more dancing around with sophistry.

    It might make you feel better to know that, “proofs of ID” are equally fallacies. Only you hardly see any of those while the internet is full of “proofs of evolution”. Which are fallacies as you must admit.

  12. petrushka: The problem with the OP is that evolution is not proven true of false by syllogisms; it is supported or undermined by evidence.

    You have a reading comprehension problem too?!?

    I clearly stated:
    “This particular OP is NOT saying “evolution is false”. Of course “evolution” is false, but for OTHER reasons, not because of this fallacy. This OP is LIMITED to “proofs of evolution are all logical fallacies”.
    Is this so hard to get?

  13. Kantian Naturalist: That sentence makes no sense. The conclusion is not “illogical”; it’s the inference which is bad or invalid.

    Fallacies are by definition logic failures. Yes, the inference is what’s discussed here. You three have reading comprehension problems?!?

    Kantian Naturalist: Now, if you want to just stipulate that you’re replacing the conditional with a biconditional — replacing the “if, then” with “if and only if, then” — then sure, then you have all the advantages of s; it is supporte.

    What’s this nonsense?

    Kantian Naturalist: What gets me is that any reasonable person would have said, “huh, ‘proofs of evolution’? Technically that can’t be right, but ok, they clearly meant ‘evidence’” rather than both make a huge case out of the supposed fallacy being committed here — and also at the same time getting the logic wrong.

    So you argue that they don’t mean “proofs” and that this is not a fallacy?
    It’s like saying you didn’t stab the victim and you didn’t kill him when you stabbed him.

  14. dazz: KN explained science relies on inference to the best explanation very early on.

    Assuming “evolution” is ‘science’. This is a FALSE assumption as discussed many times.

    Also, this OP is not about ‘evidence’ but about “proofs of evolution” that fill the internet.

    I must conclude ‘Impaired reading comprehension’ must be a condition that afflicts all Darwinistas.

  15. keiths: It can also be a bad inference when the premises are true and the conclusion is true. Sometimes bad reasoners get lucky.

    It could well be so. This OP is not about the conclusion being true or false but about the logical fallacy. Ditto “reading comprehension issues”.

  16. walto: A valid argument means that if the premises WERE true, the conclusion also has to be true.

    False!
    As explained, this particular fallacy (affirming the consequent) is made of two TRUE statements and nonetheless an ILLOGICAL conclusion:
    “If it’s raining, then the streets are wet.” – TRUE
    “The streets are wet” – TRUE
    “Therefore it’s raining” – FALSE (even though “it’s raining” may be TRUE or FALSE)

    Ditto…

  17. Nonlin.org: [quoting walto]:

    A valid argument means that if the premises WERE true, the conclusion also has to be true.

    False!
    As explained, this particular fallacy (affirming the consequent) is made of two TRUE statements and nonetheless an ILLOGICAL conclusion:
    “If it’s raining, then the streets are wet.” – TRUE
    “The streets are wet” – TRUE
    “Therefore it’s raining” – FALSE (even though “it’s raining” may be TRUE or FALSE)

    Ditto…

    No nonlin. walto is entirely correct.
    Your example (argument alpha) is a FALLACY. The fallacy of affirming the consequent.That is, it is NOT a *valid* argument.

    The following argument (argument beta) IS a valid argument, not a fallacy:
    P1 “If it’s raining, then the streets are wet.” – we agree on this one, right?
    P2 “The streets are not wet” –
    C “Therefore it’s not raining” –
    This is the contrapositive. Not a fallacy.
    It is IDENTICAL to this argument (argument gamma):
    P1 If the streets are not wet, then it is not raining.
    P2 It is raining
    C Therefore the streets are wet.
    Which in turn is identical (in form) to the following argument (argument delta)
    P1 If common descent is not true, then no consilient nested hierarchy. (Premise 1 of argument delta)
    P2 We observe consilient nested hierarchy (Premise 2 of argument delta)
    C Therefore common descent is true.

    Argument delta is a VALID argument, it is NOT a FALLACY.
    The fact that (protestations aside) you wish to dispute the truth of Premise 1 (or of Premise 2, bon chance) does not change the fact that the argument is NOT a FALLACY.
    Thus disproving the thesis of the OP.
    Once you acknowledge your error, we can move on to the truth of premise 1.
    “Reading comprehension”, indeed.

  18. Nonlin.org: affirming the consequent) is made of two TRUE statements and nonetheless an ILLOGICAL conclusion:
    “If it’s raining, then the streets are wet.” – TRUE

    Oy.

  19. DNA_Jock: No nonlin. walto is entirely correct.

    Thanks, but it’s not exactly a big deal. The definition of “validity” can usually be found somewhere in the first paragraph of page 1 of every intro to logic text. That nonlin makes comment after comment contradicting that definition (and does so in his own extremely obnoxious way, throwing in a bunch of stupid insults in each post) just repeatedly points up the amazing extent of his absurdity and arrogance.

  22. DNA_Jock: Which in turn is identical (in form) to the following argument (argument delta)

    No, your Beta is NOT IDENTICAL to your Delta.
    P1 “If it’s raining, then the streets are wet.”
    IS NOT IDENTICAL TO
    P1 “If it’s not raining, then the streets are not wet.” OR, as you write:
    P1 “If common descent is not true, then no consilient nested hierarchy.”

    They would ONLY be identical “IF AND ONLY IF” rain…wet. And this is your mega error.

    Anyway, you admit Alpha is a fallacy and this is what the OP deals with, not Beta, not Delta. For the record, this is Alpha:
    “If it’s raining, then the streets are wet.” – TRUE
    “The streets are wet” – TRUE
    “Therefore it’s raining” – FALSE (even though “it’s raining” may be TRUE or FALSE)

    So once again, your “argument” fails. But kudos for trying, which is a LOT MORE than can be said about all other touchy-feely displeased comments on this extremely long thread to a very clear and simple topic.

  23. DNA_Jock: Thus disproving the thesis of the OP.

    You’re desperate and not making any sense.

    Let’s do it differently.
    YES or NO – are these Affirming the Consequent fallacies:
    a1. If Bill Gates owns Fort Knox, then Bill Gates is rich. Bill Gates is rich. Therefore, Bill Gates owns Fort Knox. False!
    b1. If an animal is a dog, then it has four legs. My cat has four legs. Therefore, my cat is a dog. False!
    c1. If it’s raining, then the streets are wet. The streets are wet. Therefore it’s raining. False! It could be raining or it could be something else. The “therefore” claim is false.

    a1? b1? c1? FALLACIES YES or NO?

    EXACTLY HOW are those different than:
    a. If “evolution” is true, some fossils are ancestors of and therefore resemble existing organisms. Fossils resemble one another and existing organisms. Therefore “evolution” is true. This argument fails because there will always be some resemblance between two or more entities (even chairs and cats have four legs in general). Also, a fossil can always be from an unrelated branch of the “tree of life” which circularly presupposes “evolution” anyway.
    b. If “evolution” is true, organisms are genetically similar. Organisms are genetically similar. Therefore “evolution” is true. This argument is false because other hypotheses such as common design account for genetic similarities just as well.
    c. If “evolution” is true, one might expect common embryology. Similar organisms have similar embryology. Therefore “evolution” is true. This fails because embryology is expected to match genetics and morphology, hence the previous counterargument applies.
    d. If “evolution” is true, one might expect vestigial organs. What looks like vestigial organs can be observed. Therefore “evolution” is true. This fails because what if those organs are useful rather that “vestigial”? And why would “evolution” not do away with “vestigial” organs as soon as they become useless? In sum, why can’t these organs have another reason or origin than “evolution”?
    e. If “evolution” is true, one expects adaptability such as antibiotic resistance. Antibiotic resistance is observed. Therefore “evolution” is true. This fails because adaptabilities such as antibiotic resistance are compatible with other hypotheses, not just “evolution”. In addition, antibiotic resistance is ubiquitous, limited, reversible, and never observed to result in organism transmutation aka “evolution”.

    To sum:
    a1, b1, c1 FALLACIES?
    a1, b1, c1 versus a-e? HOW DIFFERENT (in logic)?
    DO NOT reply with any other contorted bullshit

  24. Oh nonlin, I suspect that the penny has dropped.
    What do you think of argument gamma — you failed to mention it.
    😀

    Here is another way to illustrate your error (and it has the added benefit that it will drive phoodoo insane)

    You list three examples of the affirming the consequent fallacy — Bill Gates, your cat, and the ever-popular wet streets.
    Each of these examples is an example of the affirming the consequent fallacy.
    Here’s what I want you to do: insert a negation into BOTH terms of the opening conditional, as in “If Bill Gates does NOT own Fort Knox, then Bill Gates is NOT rich.”
    Bill Gates is rich; therefore Bill Gates owns Fort Knox. Now in each of your examples, inserting these negations makes the opening premise P1 more or less loony-tunes, but (AND THIS IS HOW PROPOSITIONAL LOGIC WORKS) it also makes the arguments NOT FALLACIES, but examples of modus tollens
    You may wish to dispute the truth of P1, but the logic that follows from P1 is unassailably correct.

    You offered up this fallacy

    Another excellent example of this logical fallacy. Thanks.

    If “evolution” is true, organisms show patterns of similarities and differences. We observe patterns of similarities and differences. Therefore “evolution” is true.

    and I fixed it (logically) by inserting negations into the opening conditional.
    A simple point which continues to wooosh over your head. Which would be forgivable and all, if this were not a thread that you had authored about fallacies in propositional logic.
    Oh dear, indeed.

  25. Nonlin.org: If “evolution” is true, some fossils are ancestors of and therefore resemble existing organisms. Fossils resemble one another and existing organisms. Therefore “evolution” is true.

    But I don’t see anybody making that argument. So what’s the point?

  26. DNA_Jock: Here is another way to illustrate your error (and it has the added benefit that it will drive phoodoo insane)

    World’s shortest road trip.

  27. DNA_Jock: You offered up this fallacy

    Another excellent example of this logical fallacy. Thanks.

    If “evolution” is true, organisms show patterns of similarities and differences. We observe patterns of similarities and differences. Therefore “evolution” is true.

    and I fixed it (logically) by inserting negations into the opening conditional.

    Then you admit this is a fallacy?
    Then you DO agree with the OP?!?
    What do you mean you “fixed it”? And for whom did you “fixed it”?

    You did reply with “more contorted bullshit”. Why can’t you keep your story straight?

    Let’s try again:
    a1, b1, c1 FALLACIES?
    a1, b1, c1 versus a-e? HOW DIFFERENT (in logic)?
    DO NOT reply with any other contorted bullshit

    Neil Rickert: But I don’t see anybody making that argument.

    Uncover your eyes and look up the links provided… somewhere in this very long thread.

  28. Nonlin.org: What do you mean you “fixed it”? And for whom did you “fixed it”?

    I agree with you. I think he has no idea what or why he fixed anything.

    Apparently Jock believes if he completely changes an argument, he can then complain that its all wrong.

  30. phoodoo: Apparently Jock believes if he completely changes an argument, he can then complain that its all wrong.

    You mean much like you do when you pretend not to understand the concept of fitness?

  31. Ack.
    Let’s keep it simple.
    Do you, nonlin, agree that if you take an argument that is an example of the “Affirming the Consequent” fallacy and you negate both statements in the opening conditional (for example, changing “If George is a cat, then George has four legs” into “If George is a not a cat, then George does not have four legs”, then you have converted a fallacious argument into a valid* argument (modus tollens, in fact).
    And that this is true for ANY example of Affirming the Consequent.
    Here is with P’s and Q’s
    Affirming the Consequent Fallacy:
    P1: If P then Q
    P2: Q
    C: Therefore P
    HOWEVER
    Modus Tollens
    P1: If not-P then not-Q
    P2: Q
    C: Therefore P

    So I “fixed” your argument by turning your example of Affirming the Consequent into an example of modus tollens.
    which is a logically valid* argument
    Here’s a pro-tip:
    The validity* of an argument does NOT depend on the truth of the premises.
    Consequently, the validity* of an argument does NOT depend on phoodoo’s, nor nonlin’s, opinion of the truth of the premises.
    Please provide us with at least an inkling that you are capable of abstract thought.

    *technical term, look it up

  32. DNA_Jock,
    Continuing this with him is so silly. He doesn’t know what “valid” means but he’s got opinions on everything.

  33. DNA_Jock: Let’s keep it simple.

    No, you’re not keeping it simple! You’re complicating (contorted bullshit) to get out of the clear logic of this OP.

    This is keeping it simple – let’s try again:
    a1, b1, c1 FALLACIES?
    a1, b1, c1 versus a-e? HOW DIFFERENT (in logic)?
    DO NOT reply with any other contorted bullshit

    DNA_Jock: So I “fixed” your argument by turning your example of Affirming the Consequent into an example of modus tollens.

    What “your argument”?!? Those (a-e) are examples of Darwinist stupidity that I only CITE. Are you fixing THEIR arguments? Then, good luck with that! But what has that to do with this OP?!?

    I should not indulge you given you avoid answering the simple questions above…
    …are you even considering how stupid these are:
    “If George is a not a cat, then George does not have four legs”?!?
    “If “evolution” is not true, organisms are not genetically similar”?!?
    “If “evolution” is not true, we won’t expect common embryology”?!?
    …
    Is any of these an ACCEPTED STATEMENT as Modus Tollens REQUIRES?!?

    mo·dus tol·lens
    [ˌmōdəs ˈtälenz]
    NOUN
    the rule of logic stating that if a conditional statement (“if p then q”) is accepted, and the consequent does not hold (not-q), then the negation of the antecedent (not-p) can be inferred.

    Can you see why your “fix” won’t work?!?

  34. nonlin here’s a deal.
    To answer your question:
    yes, your a1,b1 and c1 and a-e are all examples of affirming the consequent.
    I do not think anyone has ever claimed otherwise. I certainly have not.
    Soooooo
    Will you now answer my question:

    Do you, nonlin, agree that if you take an argument that is an example of the “Affirming the Consequent” fallacy and you negate both statements in the opening conditional (for example, changing “If George is a cat, then George has four legs” into “If George is a not a cat, then George does not have four legs”, then you have converted a fallacious argument into a valid* argument (modus tollens, in fact).
    And that this is true for ANY example of Affirming the Consequent.

    All of your wittering on about whether the initial conditional is “accepted” is merely you disputing the truth of Premise 1. The modus tollens is a valid* argument, even if the initial conditional is looney-tunes.
    (Grown-ups have been known to use this rule to demonstrate, logically, that the initial conditional is false…something that you will try to do quite soon after you grasp this rule of logic. Hopefully)

  35. DNA_Jock: yes, your a1,b1 and c1 and a-e are all examples of affirming the consequent.
    I do not think anyone has ever claimed otherwise. I certainly have not.

    At least we’re clear on the basics. Of course others have claimed otherwise, else we wouldn’t be on page 10 of comments…

    DNA_Jock: All of your wittering on about whether the initial conditional is “accepted” is merely you disputing the truth of Premise 1.

    It’s not me “wittering”, it’s about properly applying the concept per the definition.

    Sorry, I just can’t see how you would convert “affirming the consequent” into “denying the consequent” (modus tollens) to “fix it”.

    Try converting
    “If P then Q.
    Q.
    Therefore, P”

    into

    “If P then Q.
    Not Q.
    Therefore, Not P.”

  36. Nonlin:

    Sorry, I just can’t see how you would convert “affirming the consequent” into “denying the consequent” (modus tollens) to “fix it”.

    Jesus, Nonlin. Jock even gave you the instructions:

    Do you, nonlin, agree that if you take an argument that is an example of the “Affirming the Consequent” fallacy and you negate both statements in the opening conditional (for example, changing “If George is a cat, then George has four legs” into “If George is a not a cat, then George does not have four legs”, then you have converted a fallacious argument into a valid* argument (modus tollens, in fact).
    And that this is true for ANY example of Affirming the Consequent.

    Let’s do this step by step.

    1. The original example of affirming the consequent:

    If P then Q.
    Q.
    Therefore, P.

    2. Negate both P and Q in the opening premise, leaving the rest of the argument unchanged:

    If not P then not Q.
    Q.
    Therefore, P.

    You now have a valid argument.

  37. keiths,

    Let me try this:

    1. If it rains, I won’t go out.

    2. I won’t go out.

    3. Therefore it rains.

    Now I negate it:

    1. If it doesn’t rain, I will go out.

    2. I will go out.

    3. There it doesn’t rain.

    Valid? Why. Who says it doesn’t rain? Where did I say if it does rain I won’t go out?

  39. phoodoo: 1. If it doesn’t rain, I will go out.

    2. I will go out.

    3. There it doesn’t rain.

    Therefore it rains?

    Now its valid?

  40. no phoodoo, follow the instructions:

    As keiths put it — “Negate both P and Q in the opening premise, leaving the rest of the argument unchanged:”

    Try again.
    For your travel plans, it becomes
    1. If it doesn’t rain, I will go out.
    2. I won’t go out.
    therefore…

  41. Ok:

    Let me try this:

    1. If it rains, I might go out.

    2. I might go out.

    3. Therefore it rains.

    Now change to :

    1. If it doesn’t rains, I might not go out. (first premise changed)

    2. I might go out.

    3. Therefore…?

    Does an ambiguous premise change anything?

  42. Actually phoodoo, the negation of “I might go out” is “I definitely won’t go out”.
    Think “The probability that I go out is non-zero” and its negation.
    Statements in propositional logic are either true or false, there is no third option. That’s one reason why science does not use propositional logic.
    [Careful, phoodoo, a trap looms]

  43. DNA_Jock: Actually phoodoo, the negation of “I might go out” is “I definitely won’t go out”.

    No its not. Why isn’t it I definitely will go out?

    DNA_Jock: Statements in propositional logic are either true or false, there is no third option.

    That is why I said ambiguous premises are not valid. And you disagreed.

  44. DNA_Jock: Actually phoodoo, the negation of “I might go out” is “I definitely won’t go out”.

    Why didn’t you say the negation is “I definitely will go in.” Or “Someone other than me definitely will go in”. Since the opposite of me is someone else.

    Because ambiguous terms can’t be validated.

  45. Jock:

    Actually phoodoo, the negation of “I might go out” is “I definitely won’t go out”.

    phoodoo:

    No its not. Why isn’t it I definitely will go out?

    Because “I might go out” is equivalent to “It’s possible that I’ll go out”. The negation of that is “It’s impossible that I’ll go out”, which is equivalent to “I definitely won’t go out”.

    Baby steps, phoodoo. You’re not ready for modal logic. Leave the “might” off and see if you can handle the following:

    If it rains, I won’t go out.
    I won’t go out.
    Therefore it rains.

    That’s invalid, and it’s an example of affirming the consequent. See if you can convert it to a valid argument by following the instructions: “Negate both P and Q in the opening premise, leaving the rest of the argument unchanged.”

  46. keiths:
    If it rains, I won’t go out.
    I won’t go out.
    Therefore it rains.

    Ok, but then we better use Jocks rules:
    1. If it doesn’t 0 percent humidity, You will go in.

    2. I won’t go out.

    3. Therefore it rains?

  47. phoodoo,

    You’ve already made a fool of yourself winging it. Time to follow the instructions.

  48. keiths:
    phoodoo,

    You’ve already made a fool of yourself winging it.Time to follow the instructions.

    According to Jock (and now you) you must negate ALL parts of the premise, so….Your rules.

    The negation of me is not me.

  49. keiths,

    In fact, if we play by your silly rules, then if I say

    1. If it rains, I definitely will go out.

    Must then be changed to :

    “If it doesn’t rain, I might not go out.” Since might is the opposite of definitely?

    Or it can be “If it doesn’t rain I might go out”, because you are picking and choosing which parts to negate.

  50. phoodoo,

    I think this is the trap Jock was talking about. Little did he realize that it was his mouth that was the trap.

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