- Quiz posted on Canvas this afternoon (Weds 11/9), due by midnight!
- Exam #2 next Friday (11/18)
- Liz's review session: Thursday 11/7, 6-8 pm, Shatzel Hall 317. Remember, I'm also available during office hours.
- John's review session: Next week, probably Tuesday 11/5, John will provide details soon.
- Be sure to let me know in advance if you are unable to take the exam at the scheduled time. Makeups require advance notice. Serious & unavoidable conflicts only!
- No class Friday (11/11)!
Plan for today:
- New material: arguments from personal incredulity
- This is first because I've got to cover it today
- Review arguments from ignorance
- Structure of argument & how to evaluate
- Legitimate vs. illegitimate (fallacious) arguments from ignorance
- Related concepts: falsifiability, burden of proof, null hypothesis, target audience, "proof," relevant experts
- Hopefully clear up confusion...
- Review HW 4.5
- IF TIME, Review HW 4.4 (Causal reasoning errors)
- Please see me during office hours to discuss questions we don't get to today!
Arguments from personal incredulity
Incredulity = def. The state of being unwilling or unable to believe something
Note: An argument from personal incredulity is a type of argument from ignorance. However, arguments from personal incredulity rely on a premise that states "I don't know," rather than a premise that states "No one knows."
Structure of an argument from personal incredulity
P1) I find X implausible.
C) Therefore, X is false or implausible.
If it isn't already obvious what's wrong with this argument, add the implied premise to make it valid.
What's the implied premise (enthymeme)?
Hint: modus ponens it.
Why is the implied premise problematic?
The problem with arguments from personal incredulity:
The fact that you don't believe X, you're ignorant of X, or you don't understand X is usually not a good reason to conclude that X is false, or highly improbable.
New term - epistemic humility
Basically means realizing your knowledge is limited
E.g., Socrates is wise because he knows how much he doesn't know
Examples of arguments from personal incredulity
- I don’t understand how life can just move from bacteria to humans all on its own. There had to be an intelligent designer behind it! [Subtext: evolution must be false!]
- I don't believe that .999... = 1, so it can't be true!
Regarding the second example, mathematicians will tell you this is true. I still can't wrap my brain around it, but here's a proof (via iflscience.com):
More crazy math facts here As these examples illustrate, an argument from personal incredulity usually indicates lack of knowledge, lack of effort to uncover information, lack of imagination, bias, etc. on the part of the arguer.
It's safe to assume such arguments are fallacious whenever the personal view expressed is contrary to that of experts.
Example from Homework 4.5:
7. I simply can't believe the God would allow the earth to overheat, therefore climate change must be false. (Paraphrasing Senator James Inhoff).
In class exercise:
a) Put this argument in standard "argument from personal incredulity" form. Include the enthymeme as P2!
b) Assess the premises (acceptable, unacceptable, questionable).
c) Give your overall assessment of the argument.
d) *Extra credit/for funsies - Formalize Inhoff's argument in support of P1, i.e., his disbelief in global warming.
Hint: make it a valid, deductive argument (modus ponens). Then, assess this sub-argument's premises and its overall strength.
If you're feeling confused at this point, here's a short video that explains arguments from personal incredulity quite nicely (though it's a bit boring):
Review: Arguments from ignorance
Basic structure
Formulation #1:
X is true because no one's proved that X is false
P1) No one's proved that X is false
C) Therefore, X is true
Formulation #2:
X is false because no one's proved that X is true
P1) No one's proved that X is true
C) Therefore, X is false
[Fallacy ref confirms this formulation has the same problem]
A word about proof: Many arguments from ignorance rely on the assumption that the standard for proof is "beyond a shadow of a doubt." But this is an unreasonable standard of proof. The arguments we're considering are inductive and thus, the conclusion is always probabilistic. Accordingly, the proper standard of proof is something like, "Our best theories, evidence, and expert consensus support X conclusion." When I use the term "proof" it should be taken to imply "proof" in the latter sense.
Our formal structure (BGSU PHIL 1030 structure) for arguments from ignorance is modified to indicate that the argument is inductive, i.e., probabilistic, and that evidence in support of the conclusion should come from the right kinds of sources (relevant experts). We reconstruct arguments from ignorance as two premise arguments.
Formulation #1:
X is true because no one's proved that X is false
P1) There's no proof (i.e., no good evidence) that X is false
P2) There's been a reasonable search for the relevant evidence by whoever is qualified to do so (often experts)
C) Therefore, X is probably true
Formulation #2:
X is false because no one's proved that X is true
P1) There's no proof (i.e., no good evidence) that X is true
P2) There's been a reasonable search for the relevant evidence by whoever is qualified to do so (often experts)
C) Therefore, X is probably false
Arguments from ignorance are often, but not always fallacious (bad) arguments.
Inductive, scientific arguments often take the form of a legitimate (cogent) argument from ignorance:
P1) No one's proven (i.e. there's no good evidence) that vaccines cause autism.
P2) There's been a reasonable search by the relevant experts for evidence that vaccines cause autism.
C) Therefore, vaccines probably don't cause autism.
Notice that in this example the argument goes through because we commonly accept that the person who wishes to challenge scientific consensus bears the burden of proof. That is, it's on the challenger to provide positive evidence that can change our minds.
How to differentiate legitimate, i.e., cogent, from illegitimate, i.e., weak, arguments from ignorance:
- Assess P1 and P2 to see if they are acceptable, unacceptable, or questionable.
- If P1 and/or P2 is/are unacceptable (or highly questionable), the argument is fallacious.
General guidelines:
- Generally, if an argument from ignorance takes the following form it's bad:
There's no evidence that X doesn't exist, therefore it does.
Or (same thing, different wording):
You can't prove that X doesn't exist, therefore it does.
Explanation: The arguer is making a non-falsifiable claim. You can't prove something exists with the absence of evidence; otherwise we could prove absolutely anything exists.
- Generally, the burden of proof falls on the person making an existential claim.
- That is, if you want to claim that something exists or that some variable explains an observation, the burden is upon you to provide evidence for it.
- Otherwise, the reasonable position is the null hypothesis. The null hypothesis just means that we assume no entity or phenomena exists unless there is positive evidence for its existence.
- Generally, the burden of proof in an argument rests on a person who challenges expert/theoretical consensus (or, in some cases, the consensus common knowledge supports).
- A note regarding evidence: The evidence should be something the target audience can accept. A safe way to proceed is to assume that you're trying to persuade a universal audience.
- Keep in mind that there are different kinds of evidence
- Direct evidence (roughly, what we've been calling positive evidence): the evidence directly supports a conclusion, no inference required
- I see Professor Plum kill Mr. Body
- Indirect evidence (in law this is called circumstantial evidence): the available evidence supports an inference to the conclusion
- Professor Plum had motive, he was the only one present when Mr. Body died, and he's got blood all over his clothes
(paraphrased from this source)
Both direct and indirect evidence can provide strong support for a conclusion.
On that note, consider an example from the homework:
3. There's no evidence of life in the universe besides on earth, therefore there probably isn't any life elsewhere in the universe.
Groups:
a) Put the argument in standard "argument from ignorance" form
b) Assess the premises for acceptability
c) Provide an overall assessment of the argument's strength
Let's all take a minute to ponder the fact that someone knitted this for his/her cat.
Homework 4.5 Review, continued
(questions not covered above)
a) Put the argument in standard "argument from ignorance" form
b) Assess the premises for acceptability
c) Provide an overall assessment of the argument's strength
1. Aliens are visiting us since no one has proven that they aren't.
2. There's no good evidence to believe aliens are visiting us, therefore they haven't.
4. You can't prove that CERN particle collider won't cause a tear in the space time fabric leading to the end of the universe, therefore it will.
5. There's evidence you don't understand arguments from ignorance, therefore you can understand how to evaluate this question.
6. No one has ever disproven Bigfoot's existence, therefore, he probably exists.
Lesson 4.4 (Review)
1) General structure of a causal argument
2) Common errors in causal reasoning
1) General structure of a causal argument:
P1) X is correlated with Y.
P2) The correlation between X and Y is not due to chance (i.e., it is not merely statistical or temporal).
P3) The correlation between X and Y is not due to some mutual cause Z or some other cause.
P4) Y is not the cause of X. (Direction of causation.)
C): X causes Y.
*In P2, to show the correlation between X and Y is not due to chance, there should be a (plausible) proposed causal mechanism.
2) Common errors in causal reasoning
A causal argument or explanation is strong to the degree that we are willing to accept each of the four premises. If we find one or more of the errors listed below we should be less confident about the affected premise(s).
1. Post hoc ergo propter hoc (after therefore because of)--usually referred to just as "post hoc fallacy").
-Confusing causation with temporal order.
-Just because Y happened after X it doesn't follow that X caused Y. -This error applies to (P1), (P2), and (P3).
"After a black cat crossed my path, I failed my critical thinking exam. That cat caused me to fail!"
 |
| U failed lol |
2. Misidentifying the Relevant Causal Factor(s)
-There are often hundreds of factors common to each causal event. It does not follow that they are all relevant.
-Misidentifying the relevant causal factor is usually a consequence of not having enough knowledge of the topic at hand.
-This error applies to (P1), (P2), and (P3).
Clueless pet owner #1: "I know she's a bit heavy... I read that her breed puts on weight easily."
Veterinarian: "Yes, beagles do put on weight rather easily. But genetics are not the main reason your dog resembles a bloated coffee table. The relevant causal factor is how much you're (over)feeding her."
3. Mishandling Multiple Factors:
-For every general causal argument there will often be many antecedent variables involved.
-Identifying the one that has causal import can be tricky.
-People will often fail to consider alternative - and perhaps more plausible - causal variables to the one(s) they identify.
-This error applies to (P1), (P2), and (P3).
Clueless pet owner #2: "My cat is really itchy. I think she has a grass allergy/food allergy/sensitive skin because she's a Scorpio..."
Veterinarian: "Is she on flea prevention?"
C.O. #2: "No way. That stuff is full of chemicals!"
Veterinarian: "Yeah..."
4. Confusing Correlation and Causation (Cum hoc ergo propter hoc="comes with therefore because of")
-Just because two events or variables are correlated or co-occur, it doesn't follow necessarily that there's a causal relationship.
-Often a good way to avoid committing this error is to see if you can come up with a likely causal mechanism. If you can't then it's likely simply correlation.
-This error applies to (P2) and (P3).
5. Confusing Cause and Effect (aka Direction of Causation). -Often it is difficult to disentangle the direction of causation. Does X cause Y, or does Y cause X?
-This error applies to (P4).
E.g., "Alcohol abuse causes depression."
What's the alternative direction of causation? Is it equally plausible?
Less plausible:
6. No Control (see Mill's Methods: Method of Difference).
-Often misattributions of causation occur because there is no control group.
-E.g., If we don't know the natural prevalence rate of a disease or its average natural healing time we cannot reasonably attribute causal power to a purported remedy.
-Applying a control helps eliminate errors in (P1), (P2), (P3), and (P4).
Specific to medical/health-related research: Need to control for the placebo effect.
Lesson 4.4 - Review selected homework questions
I. (a) Identify the proposed cause and effect. (b) Suggest alternative explanations. (c) Suggest which premise of a standard form causal argument the original explanation fails and name the error.
Example:
Frank reads a lot and wears glasses therefore reading a lot must cause permanent eyesight damage.
(a) Reading a lot caused Frank to lose his eyesight.
(b) Genetic factors might also explain why Frank's eyesight is poor.
(c) This argument would fail Premise 2 because it commits confusing causation with correlation (cum hoc ergo proptor hoc).
1. Mary is feeling sick. She ate about 2 hours ago, it must be something she ate.
2. Did you hear about the pipeline rupture last week? I'll bet those anti-pipeline protestors sabotaged it in order to make everyone afraid of pipelines.
3. I feel hungry. That explains why I feel so tired.
5. He got his well-paying job because he dresses well.
6. Violent video games cause children to be violent.
7. You shouldn't smoke the pot. My friend smoked the pot and now he has a mood disorder.
9. Bob sexually harassed his co-worker because he watches pornography.
III. Critical Thinking in the Real World
As part of the war on drugs, Black and Hispanic citizens (especially men) are subject to stop and frisk at disproportionately higher rates than white citizens. Black and Hispanic drivers are also pulled over at disproportionately higher rates as part of the war on drugs.
Police and others explain their behavior by pointing to incarceration rates. That is, the fact that more Blacks are arrested and convicted for drug crimes causes police officers to scrutinize them more. For every white male in prison there are 6 Black males, about 60% of which are there for drug crimes (mostly minor). It turns out, however, that Blacks and whites use and sell drugs at approximately the same rate (within a percent). Think about direction of causation and feedback loops to explain why it is both true that Blacks and hispanics are arrested and convicted of drug crimes at higher rates that whites even though there's no difference is rates use or selling.
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