Evolution affirms the Consequent

  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. It’s too bad the comment plugin won’t accept html tables.

    Here’s a summary for Nonlin and phoo:

    1. Good logic + true premises = a valid argument, a sound argument, and a true conclusion.

    2. Good logic + false premises = a valid argument, an unsound argument, and an unreliable conclusion.

    3. Bad logic + true premises = an invalid argument, an unsound argument, and an unreliable conclusion.

    4. Bad logic + false premises = an invalid argument, an unsound argument, and an unreliable conclusion.

    Sound arguments yield true conclusions. Unsound arguments may or may not.

    An argument is valid if the logic is good, whether or not the premises are true.

    A sound argument requires good logic and true premises.

  2. colewd: Thus we can’t really just make any claim, say if it is true something else is also true and then claim that is logical. It’s on more coherent than saying ‘if blue is good ‘ five no longer equals nine.

    I think the error is that the second statement does not follow from the first.

    Exactly. This is what I mean by the premise being incoherent. Its not a question of the premise being true or the argument structure being valid, it is a problem of the first premise is itself invalid.

    “If birds can fly my aunt was a soldier. ” The premise is neither true or untrue, so we don’t need a second step.

  3. If it does not have four legs it is not a table
    It is not a table
    Therefore…

  4. I have spent more time than I wished writing SQL queries. I have just enough intelligence to understand what they need to do, and to test them and make them work, but not enough to write complex queries in one try.

  5. keiths:
    Flint,

    We’re trying to get Nonlin (and phoodoo) to understand the difference between validity and soundness.

    Yes. As I wrote earlier, it is difficult to get a man to understand something when his religion depends on his NOT understanding it. Logical errors can sometimes be hard to spot, but soundness errors can be impossible. As far as I can tell, the creationist argument always starts out

    The creationist god exists
    That god would do (or would not do) x
    Therefore either those who don’t see x are blind (in the first case), or those who see it are deluded (in the second).

    NOW, the challenge is to get past wildly unsound premise 1. So long as we remain stuck there, the notion of an unsound premise will be incoherent.

  6. Flint: NOW, the challenge is to get past wildly unsound premise 1.

    Premises can’t be unsound. Only arguments can.

  7. phoodoo,

    “If birds can fly my aunt was a soldier. ” The premise is neither true or untrue, so we don’t need a second step.

    Birds can fly, so the premise is true if your aunt was a soldier. Was she?

  8. keiths:
    phoodoo,

    Birds can fly, so the premise is true if your aunt was a soldier.Was she?

    Some birds can’t fly. So the premise is neither true nor untrue.

    And my aunt could be a soldier or not a soldier, regardless if some birds can or can not fly.

    Maybe this is why many of your arguments fall flat, and yet you keep arguing them. Like that if you offer someone chocolate or vanilla ice cream, that is evidence we can choose. Its not.

  9. phoodoo,

    “Birds can fly” is not equivalent to “every bird can fly”. “Humans can walk” is not equivalent to “every human can walk”.

    Logic — you’re doing it wrong.

  10. keiths,

    Right, we don’t know what is meant by birds flying, nor by what is a soldier, nor do we know why there is any correlation. Thus the premise itself is not valid, not the structure of the argument.

  11. walto: Premises can’t be unsound. Only arguments can.

    If there is an experimental philosopher in the house, this thread would seem to offer some research possibilities on people’s intuitions regarding the premises in Huemer’s argument.

  12. No phoodoo, you really are doing logic wrong.
    If we use a valid argument and arrive at a conclusion that is false, then we can safely deduce that one of our premises (don’t know which) is false.
    See proof by contradiction
    If we use an invalid argument (a fallacy, for example), we cannot safely deduce anything.
    See if you can understand keiths’s four numbered scenarios at the top of this page.
    We can demonstrate this with your aunt.
    1) If birds can fly my, aunt was a soldier
    2) My aunt was not a soldier
    3)Therefore birds cannot fly
    The logic is valid.
    We observe a flying bird, and we deduce that one of our premises is false: either my aunt was a soldier or premise (1) is false.
    HOWEVER
    1) If birds can fly, my aunt was a soldier
    2) My aunt was a soldier
    3)Therefore birds can fly.
    This logic is invalid. This is the fallacy of affirming the consequent.
    Coherence and correlation[!] don’t enter into it.

  13. DNA_Jock,

    No, sorry mathematician.

    Let me make it easier for you.

    “If birds can fly…”

    There is a bird that can not fly, so the statement that birds can fly is not technically true or not true. Its no more true than saying women can swim, or men can play guitars. Some can and some can’t. Therefore, the statement, “birds can fly” is not a true statement, nor is it a false statement, anymore than men can play guitars. I know a man that can not play a guitar, so the statement that men can play guitars can be untrue.

    Get it numbers man?

  14. phoodoo: There is a bird that can not fly, so the statement that birds can fly is not technically true or not true. Its no more true than saying women can swim, or men can play guitars. Some can and some can’t. Therefore, the statement, “birds can fly” is not a true statement, nor is it a false statement, anymore than men can play guitars. I know a man that can not play a guitar, so the statement that men can play guitars can be untrue.

    None of that matters in this case. He could have used

    If farley balarleys, then my aunt is a kuffnagle.

    That’s why, in propositional logic, ps and qs are often used. What matters for purposes of whether an argument is valid is IF something is (or were) true then blah blah. Not THAT it’s true.The truth, falsity or nonsensicality of any included proposition doesn’t affect the validity of this type of argument.

  15. walto: The truth, falsity or nonsensicality of any included proposition doesn’t affect the validity of this type of argument.

    Pearls/Swine

  16. phoodoo: Therefore, the statement, “birds can fly” is not a true statement, nor is it a false statement

    Next up: fish can swim? Not true!

    I am certainly learning a lot about logic today.

  17. phoodoo:
    keiths,

    Right,we don’t know what is meant by birds flying,nor by what is a soldier,nor do we know why there is any correlation.Thus the premise itself is not valid,not the structure of the argument.

    Premises are never either valid or invalid. Those are properties of arguments or syllogisms or deductions. Simply, something being valid means that IF the premises were true (doesn’t matter whether they actually ARE) the conclusion would also have to be true. Valid arguments are truth-retaining in that way. Sound ones are valid arguments having only true premises.

    So, again, no premise can be sound, unsound, valid or invalid–though the way you may have gotten to some premise may have been through any of those methods of reasoning.

    (Once you grok this, go back and look at your comments on this thread. I think you’ll start to see what others have been objecting to.)

  18. walto: The truth, falsity or nonsensicality of any included proposition doesn’t affect the validity of this type of argument.

    Quite so. But I doubt Nonlin is interested in learning anything about how logic actually works — that requires far too much intellectual discipline. Nonlin’s contributions at TSZ indicate an mind that has absorbed a good deal of information but has no ability to prevent elementary confusions from arising because their mind lacks discipline. It’s good of you to try, but some folks just aren’t educable.

  19. DNA_Jock: Nonlin.org: Demonstrate this if you want to move on.

    Let’s look at YOUR example in a neutral light:
    1) If it doesn’t rain, the streets are not wet
    2) The streets are wet
    3) Therefore it does rain

    Does this make any sense to you?

    Err, yes.

    So you don’t think the streets can be wet for other reasons? Washing, broken pipes, heat wave relief, water cannons, etc? Seriously?

    And when will you demonstrate (prove)?

  20. Corneel: You said that this OP was dealing with the logic fallacy, not with the truth of the premises. Have you changed your mind?

    No. Why are you asking?

    DNA_Jock: From nonlin, I just expected off-topic huffing and puffing, à la cordova. I did NOT expect nonlin to crash so badly. That’s sobering, given the OP.

    In your world, strong feelings make strong arguments. Now back to earth. Do you have any valid argument?

    Kantian Naturalist: The easiest way to understand modus tollens is to see that it is extensionally equivalent to modus ponens

    Good for you. But let’s not forget that none applies if not “accepted statement”.

  21. Kantian Naturalist: Quite so. But I doubt Nonlin is interested in learning anything about how logic actually works — that requires far too much intellectual discipline. Nonlin’s contributions at TSZ indicate an mind that has absorbed a good deal of information but has no ability to prevent elementary confusions from arising because their mind lacks discipline. It’s good of you to try, but some folks just aren’t educable.

    You believe a valid argument can contain a premise which can be both true and untrue at the same time?

  22. Nonlin.org: So you don’t think the streets can be wet for other reasons?

    Baby steps, nonlin.
    You wish to dispute the truth of the first premise.
    Before we get to THAT, you need to acknowledge that the argument is entirely valid — that there is no “fallacy” here: if the premises are true, then the conclusion follows.

    If not R, then not W.
    W
    Therefore R

    Remember, you wrote [in reference to affirming the consequent]:

    Understand that this particular OP deals only with this particular logic fallacy.

    I really thought you were smarter than this.

  23. phoodoo: You believe a valid argument can contain a premise which can be both true and untrue at the same time?

    Oh phoodoo, it is one of the axiomatic Laws of Thought that such statements do not exist. That sort of talk would get you banned from Uncommon Descent, 😀

  24. colewd: I think the error is that the second statement does not follow from the first. Evolution has not been demonstrated to be the sole cause of similarities and differences. This is simply Darwins inference.

    Hang on. I smell a missing gene or something that turns these guys into logic-less Darwinistas. Let’s explore further and see what’s wrong with them.

    petrushka: In the world I live in, we say:

    If the driveway is not wet, it hasn’t rained.
    The driveway is not wet
    Therefore, it hasn’t rained.

    And that works 99% of the time but it fails sometimes. Can you acknowledge that? Also, let’s not confuse ‘rain’ with “evolution”.

    Flint: Again, I’m not sure I’m following all this logic. Let me try…

    If it rained, the streets are wet.
    The streets are wet.
    Therefore it rained!

    This strikes me as wrong. Sure rain will wet the streets, but other things can also wet the streets. And therefore, if the streets are wet, we can hypothesize that rain was the cause, but that hypothesis must be tested. It can’t be inferred.

    I think of this as inference not being reversible. p->q does not imply q, therefore p. This was presented to me in grade school as:

    All tables have four legs
    A cat has four legs
    Therefore, a cat is a table.

    Exactly! Caution: Darwinistas appear immune to logic.

    keiths: Your first example is both invalid and unsound. It’s invalid because it violates the rules of logic, and it’s unsound because it’s invalid. To be sound, it would need to be valid and its premises would also need to be true.

    Your second example is also invalid and unsound.

    The third example is valid but unsound. The logic is correct, but the first premise is untrue:

    ONLY tables have four legs.

    The false premise renders the argument unsound.

    How is any of these disagreeing with the OP?

  25. keiths: Sound arguments yield true conclusions. Unsound arguments may or may not.

    An argument is valid if the logic is good, whether or not the premises are true.

    I never used the word ‘sound’ in this OP.

    ‘Valid’ is [correctly] used only here:
    “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]:”

    …and here

    “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.”

    Now, which one of these two sections is not to your liking and why?

  26. Kantian Naturalist: Quite so. But I doubt Nonlin is interested in learning anything about how logic actually works — that requires far too much intellectual discipline. Nonlin’s contributions at TSZ indicate an mind that has absorbed a good deal of information but has no ability to prevent elementary confusions from arising because their mind lacks discipline. It’s good of you to try, but some folks just aren’t educable.

    I think I disagree with this. His confusion isn’t elementary or undisciplined. Instead, it arises from the conflict between what IS actually true and what MUST be true according to his faith. If logic fails to uphold his faith, logic is wrong. If premises fail, those must be wrong. If reality fails, reality must be inherently ambiguous or inconsistent. But the faith MUST be supported.

    I’ve noticed that nonlin seems quite coherent and thinks quite clearly, when his faith is not threatened. His faith, alas, rests on his NOT understanding rules of inference in those cases.

  27. Flint: Yes. As I wrote earlier, it is difficult to get a man to understand something when his religion depends on his NOT understanding it. Logical errors can sometimes be hard to spot, but soundness errors can be impossible. As far as I can tell, the creationist argument always starts out

    And what about the atheistic religion?
    Also, this particular OP deals with “evolution” and not at all with “creation”, so what’s your point?

    Kantian Naturalist: walto: The truth, falsity or nonsensicality of any included proposition doesn’t affect the validity of this type of argument.

    Quite so. But I doubt Nonlin is interested in learning anything about how logic actually works

    You misinterpreting. Did I not say:
    “This particular fallacy is made of two TRUE statements and nonetheless an ILLOGICAL conclusion:”?

    …AND…

    “What happens if one of the statements is FALSE or DUBIOUS such as “If “evolution” is true, blah blah blah” or “vestigial organs can be observed”?
    NOTHING. The fallacy is still present as long as the “if and only if” condition is not met when applied to two TRUE statements in this particular construct”?

    Do you have a point?

  28. walto: Premises are never either valid or invalid. Those are properties of arguments or syllogisms or deductions.

    Agree. Is this different than the OP states?

    DNA_Jock: You wish to dispute the truth of the first premise.

    No, I do not! How can you miss it so badly?!?

    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?

  29. Nonlin.org: Agree. Is this different than the OP states?

    I was replying to phoodoo. Are you megalomaniacal as well as logically illiterate and extremely unpleasant?

  30. walto,

    Do you care to answer-can a valid argument contain premises which can be both true and untrue?

  31. Flint: His confusion isn’t elementary or undisciplined. Instead, it arises from the conflict between what IS actually true and what MUST be true according to his faith.

    Say more – this is so funny. Are you schooled by Dr Fraud? Can you do hypnosis through the DNS? VPNs?

  32. DNA_Jock,

    Would it have killed you to read the first paragraph:

    However, such classical ideas are often questioned or rejected in more recent developments…

    Aristotle doesn’t get the last word.

  33. DNA_Jock: the argument is entirely valid — that there is no “fallacy” here: if the premises are true, then the conclusion follows.

    If not R, then not W.
    W
    Therefore R

    How about this:
    “If not Rain, then not Wet.
    Wet
    Therefore Rain”

    AND

    If not Water Cannons, then not Wet.
    Wet
    Therefore Water Cannons”

    What do you know? When streets are Wet it BOTH Rained and Water Cannons were used! AND the Main Pipe was also broken. AND they were also Washing the streets. Wow!

    How about “if and only if” instead?

  34. ROFL
    nonlin

    1) If it doesn’t rain, the streets are not wet
    2) The streets are wet
    3) Therefore it does rain

    Jock

    Yup

    nonlin

    So you don’t think the streets can be wet for other reasons?

    Jock

    You wish to dispute the truth of the first premise.

    nonlin

    No, I do not! How can you miss it so badly?!?

    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”.
    What you are unable to wrap your brain around is the argument I am presenting:
    IF IT IS THE CASE THAT
    1) If it doesn’t rain, the streets are not wet (premise 1)
    AND ALSO
    2) The streets are wet
    THEN INEXORABLY
    3) Therefore it does rain

    Similarly, your second argument is valid, and concludes that there are water cannons. The issue is that premise 1 of your second argument assumes a lot of water cannons.
    Until you acknowledge that this is a valid argument “if 1 and 2, then 3” then you will get nowhere.
    You are displaying a phoodooesque inability to think conceptually. And you authored an OP about logical fallacies. Oh dear.

  35. phoodoo:

    Do birds fly Jock?

    In Phoodoo World, “do birds fly?” is a gotcha question.

    Too funny.

  36. Just re-read the OP.

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

    The if then statements are not presented as logical proofs; they are presented as entailments. This has been gone over ad nauseum, but here it is again.

    Long lists of entailments are supportive evidence, not proof.

    1. If it is raining right now, I can look out the window and see rain.
    2. If it is raining, the ground will be wet.
    3. if it is raining, the weather radar will show it.
    4. If it is raining, I can stand outside and feel water drops.

    Having seen a few movies, I can propose that all of the entailments could be true without proving it is raining.

  37. Nonlin.org: “This particular fallacy is made of two TRUE statements and nonetheless an ILLOGICAL conclusion:”?

    That sentence makes no sense. The conclusion is not “illogical”; it’s the inference which is bad or invalid. There’s a tight relationship between goodness of inference and preservation of truth: a good inference will not have true premises and false conclusion.

    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.

    This is because the basic form of a deductively valid inference is “if the premises were true, then the conclusion would have to be true”. That’s the beating heart of the if, then or conditional.

    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 theft over honest toil.

    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.

  38. phoodoo,

    Jock already answered it. The sentence might be “true and untrue” if interpreted in different ways, but no proposition can be both true and false. The sentence simply expresses more than one proposition when differently interpreted. So the validity/invalidity could (likely will) vary with the interpretation of the premises.

  39. walto,

    walto:
    phoodoo,

    Do birds fly?

    Jock already answered it. The sentence might be “true and untrue” if interpreted in different ways, but no proposition can be both true and false. The sentence simply expresses more than one proposition when differently interpreted. So the validity/invalidity could (likely will) vary with the interpretation of the premises.

  40. petrushka:
    Just re-read the OP.

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

    The if then statements are not presented as logical proofs; they are presented as entailments. This has been gone over ad nauseum, but here it is again.

    Long lists of entailments are supportive evidence, not proof.

    1. If it is raining right now, I can look out the window and see rain.
    2. If it is raining, the ground will be wet.
    3. if it is raining, the weather radar will show it.
    4. If it is raining, I can stand outside and feel water drops.

    Having seen a few movies, I can propose that all of the entailments could be true without proving it is raining.

    You’re not the first to point this out. KN explained science relies on inference to the best explanation very early on. Nonlin is simply impervious to reason. I know it won’t happen, but I would revoke his publishing rights until he’s shown he understands basic logic.

  41. phoodoo: Ok. Omagain, do birds fly?

    Sure they do. But I’m not five years old. Taken that look at yourself yet?

    phoodoo: Damn, I look good!

    As I have noted many times, the more you stare into the abyss the more it stares back into you. Playing this game cannot help but rub off on you.

    But, continue, continue….

  42. 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:

    In logic and philosophy, an argument is a series of statements, called the premises or premisses, intended to determine the degree of truth of another statement, the conclusion.

    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?

  43. phoodoo: Are you calling that valid?

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

Leave a Reply