Fishing For Evidence

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Early one morning six boys came across a beautiful stream. None of them had ever tried to catch fish in this stream. Greg, one of the boys, casually looked at the stream and said, "I don't think there are any fish in there". The other boys asked, "Why not? We can't see the bottom of the stream so we can't say there are no fish". They then added, "The absence of evidence is not evidence of absence".

They decided to set up camp near the stream with the intention of spending a few days fishing and camping. They eagerly assembled their fishing tackle and set to the serious business of challenging who would catch the first or the largest or the most fish. The boys each had a preferred technique, some used live bait, some used artificial lures and some had fly fishing gear.

By lunchtime, the boys gathered at their camp. Nobody had caught a fish and nobody even reported a nibble. The mood was starting to change about catching fish in this stream. Some boys even thought Greg was right to declare there were no fish here. A short discussion about the absence of evidence ensued. One boy gave an analogy to explain the idea. He said, "Astronomers know a lot about the planet Mars. They have looked at it through the most powerful telescopes available and are unable to detect any signs of life on Mars. Being unable to detect life at such vast distance is not evidence for the absence of life on Mars."

They all agreed that they would stay and continue fishing. By sunset, still no fish had been caught. As they ate some of the tinned food they brought, the discussion turned again to the absence of evidence. Some asked, "How much absence of fish would it take to declare that there were no fish in this stream?” As the mood, along with the daylight, got darker and darker, it was decided that if no fish had been caught by lunchtime tomorrow they would pack up and find another site.

As agreed the night before, at lunchtime the boys had moved camp and declared that the absence of any evidence of fish is evidence of the absence of fish.

At the new site, which was similar to the old site, Greg mumbled something about how there probably won't be any fish here either. Everyone else groaned. Within half an hour of the first line being cast, fish were caught and Greg was happy to be proven wrong. They enjoyed their fish supper and bragged about the first to catch a fish, catching the biggest and catching the most fish and as all fishermen do, the ones that got away. Later that evening the discussion reverted to the phrase "the absence of evidence".

Greg admitted that he had no way of knowing whether there were fish at either site. He agreed that his absence of evidence was not evidence of the absence of fish. Later another boy reminded them that when they left the first site, they had all agreed that the absence of evidence was evidence of the absence of fish.  They realized, after a day and a half trying to catch fish, that by not catching any, this was evidence that there were no fish to catch.

So how can two such obviously contradictory statements as, "The absence of evidence is not evidence of absence" and "The absence of evidence is evidence of absence" both be correct? The contradiction is due to equivocation (ambiguity) over the meaning of "absence of evidence". Greg had no evidence to support his claim that there were no fish, so his absence of evidence was not evidence of absence (no fish to be caught). After spending a day and a half fishing, the boys now had some evidence that there were no fish to be caught, so the absence of evidence (no fish caught) was evidence of absence (no fish to be caught).

When anyone makes the statement, "The absence of evidence is not evidence of absence" consider carefully what they mean by "the absence of evidence". It may be necessary to ask if evidence has been sought and if it has, then the absence of supporting evidence is indeed evidence against whatever is claimed to exist.

Turning a Blind Eye

For some people, no matter how well educated they are, an ignorance of basic science or logic, an unwillingness to learn any science or logic, or an inability to criticize their own thinking, leads them to accept any explanation whether it is reasonable or just plain nonsense.

An example:
John was about four years old when he noticed two kookaburras sitting together on a fence and laughing. Two adults also saw the kookaburras. One adult said, "That means it's going to rain soon". John accepted this information because it was said by someone that John respected, and both adults seemed to take the statement seriously.

Even after John had gone through school and had been taught about the weather, in John's mind, it could still be true that kookaburras can foretell rain because animals are more "in tune" with such things whereas, scientists are still unsure. There is no cognitive dissonance [1] in John's mind because even the teacher said that our understanding of the weather is limited, as shown by our inability to accurately predict the weather. So in John's mind, the kookaburras could still be predicting rain.

There are of course many other more important issues and problems in John's life; he is after all an adult now, so his kookaburra theory is relegated to a pile of other less important ideas. Sometimes, when it has rained, John is pretty sure that he can remember hearing at least one kookaburra laughing a few days before. If he can't remember hearing any then he's sure that kookaburras must have been laughing when he wasn't around to hear them. Sometimes, John has heard the kookaburras and told himself that rain is imminent but soon forgets the forecast. In hindsight, he is pretty sure that it did rain soon after. John has even told children the theory and other adults have just smiled, so he concludes that the adults must know the theory as well.

Ken is an acquaintance of John, and when the two of them were walking along a country road, John hears some kookaburras and says to Ken, "Hear those kookaburras? We'll get rain soon". It is only when the kookaburra theory is challenged (possibly laughed at) for the first time that a cognitive dissonance becomes vaguely possible in John's mind. Other people have scoffed at his idea but John remains unconvinced by their arguments, he has used a number of defences, but now Ken is challenging his kookaburra theory.

At this point in time, John may either;
defend -

1) Argue that many other people agree with him, or
2) Relate stories of how it's happened before, or
3) Argue that it is a very old, well known principle, or
4) Argue that nobody has ever been able to disprove it, or
5) State that he was four years old when he heard it, or
6) Argue that animals are more "in tune" with the environment.

or retreat -

7) Avoid further discussion by pretending that it was meant as a joke, or
8) Change the subject to something vaguely related, e.g., "I hope it doesn't rain, I've put washing out to dry", or
9) Imply his belief as still plausible by doubting (or dismissing) Ken's refutation, e.g., "Oh, you could be right", or
10) Ignore Ken's refutation by not responding.

The six defensive arguments could be used either individually or in combination. Which ones he uses and how vehemently he defends his theory may depend on the strength of John's belief, John's opinion of Ken, and how Ken responded when John mentioned the theory.

If John thinks highly of Ken and he thinks Ken is knowledgeable then John may soften his argument and give only one explanation. In this case, John is hoping that if Ken counters this explanation, then John still knows more (as yet undisclosed) reasons that support his theory, or he could always use argument 9 to escape any further dissonance.
If John thinks Ken is not quite as knowledgeable as himself, he may defend his claim far more vigorously using all six arguments and possibly go into greater detail by citing previous experiences, trying to convince Ken.

If Ken laughed at John's claim and John respects Ken's opinion then John may be more likely to try one of the four remaining arguments. If John uses arguments 7, 8, both, or just 9, then he is unwilling to defend his claim because Ken may prove his claim is wrong. These three techniques (if used) confirm that John has had other people dismiss the theory but John has remained unconvinced.

Alternatively, if John does not respect Ken's opinion, to avoid conceding a point to Ken, John may use argument 4 or 6. These may also explain why John remains unconvinced that the theory is wrong. John may think these are his strongest arguments, because he is now challenging Ken to prove the unprovable. Or, John could just apply argument 10 and ignore Ken's response. This last argument might cause Ken to ask himself, "What does John think of my opinions? Can't be much, if he just ignores them". Ignoring someone is possibly the rudest tactic to avoid dissonance.

All of the arguments are informal fallacies, for example,

1) An appeal to the people, bandwagon fallacy. 
2) Anecdotal evidence. (A fallacious generalizing on the basis of a story that provides an inadequate sample.)
3) The fallacy of traditional wisdom.
4) An appeal to ignorance [2] (Not knowing that a statement is false is taken to be proof that it is true). John is also trying to transfer the burden of proof.
5) Whilst true, if used by itself, is a Non Sequitur [3] . If used in conjunction with another argument it is also the other argument's fallacy.
6) Assuming the answer (The thing to be proved is used as one of your assumptions). Obscurum per obscurius (Explaining something obscure or mysterious by something that is even more obscure or more mysterious.)
7) An appeal to humour (if Ken just laughed and said "Yeah sure, ha ha ha", and then John chuckled as well.)
8) Distraction, changing the subject, misdirection, diversionary tactic, digressing.
9) Appeal To Complexity (If John doesn't understand the topic, he concludes that nobody understands it. So, his opinions are as good as anybody's.)
10) Willed ignorance (I've made my mind up, so don't confuse me with more information.)

Over the years, John has not really challenged his theory, because to question the idea might discredit a long held belief and John's current model of the world fits nicely together. Instead, he has built up a series of defence mechanisms to protect his model. It is how John deals with cognitive dissonance that defines whether he is reasonable or unreasonable.

If John can't question his long held theory then he is not being reasonable, he is simply being dogmatic. Sometimes, people will go through their whole lives clinging to their beliefs despite contrary evidence. For people like John, science and logic are just matters of belief, like a religion, and those beliefs should never be challenged because doing so causes cognitive dissonance. They have reasons for holding to their beliefs, so they will assert that their beliefs are sensible.

Hopefully, John will challenge his theory and examine his ten arguments. He will recognize that they are all logical fallacies and will conclude that his theory is probably wrong. He should however keep open the idea that animals are more "in tune" with their surroundings because quite frankly, their lives depend on that awareness. Furthermore, if he is going to relate the kookaburra theory to children, he should do so as a story with a moral - Always question your beliefs. Listen to others but don't necessarily believe everything you're told.

It should be noted that nine of the ten arguments (except 6) are generally fallacious arguments irrespective of the subject matter. The falsity of these arguments is universal in that, it doesn't matter whether the theory under discussion is true or false, the arguments themselves are generally invalid. Argument 6 is an exception only because it is specific to the theory under discussion; however it is still fallacious regarding kookaburras announcing imminent rain.

To evaluate any opinion or belief, write down all the arguments that you would use (or others have used) to defend that belief. If any argument resembles a logical fallacy then discount that argument. If there are no arguments left then it's time to reconsider that belief. Never resort to any of the retreating tactics, they are rude and deceitful. If an argument is put to you that you cannot counter then at least say, "Hmm, that's a good point. I didn't think of that." and then do it!



[1] Cognitive dissonance         http://en.wikipedia.org/wiki/Cognitive_dissonance
The term used in modern psychology to describe the feeling of discomfort when holding two or more conflicting cognitions (e.g., ideas, beliefs, values, emotional reactions) simultaneously. In a state of dissonance, people may sometimes feel surprise, dread, guilt, anger, or embarrassment. The theory of cognitive dissonance in social psychology proposes that people have a motivational drive to reduce dissonance by altering existing cognitions, adding new ones to create a consistent belief system, or alternatively by reducing the importance of any one of the dissonant elements. It is the distressing mental state that people feel when they find themselves doing things that don't fit with what they know, or having opinions that do not fit with other opinions they hold. A key assumption is that people want their expectations to meet reality, creating a sense of equilibrium.

[2] Appeal to Ignorance         http://www.iep.utm.edu/fallacy/
The fallacy of appeal to ignorance comes in two forms: (1) Not knowing that a certain statement is true is taken to be a proof that it is false. (2) Not knowing that a statement is false is taken to be a proof that it is true. The fallacy occurs in cases where absence of evidence is not good enough evidence of absence. The fallacy uses an unjustified attempt to shift the burden of proof. The fallacy is also called “Argument from Ignorance.”

[3] Non Sequitur             http://www.iep.utm.edu/fallacy/
When a conclusion is supported only by extremely weak reasons or by irrelevant reasons, the argument is fallacious and is said to be a non sequitur.

A Formula 1 Straw Man?

One day at a motor racing track, two photographers were waiting for the latest model F1 car to be unloaded from the truck, to take its place next to last year's model, so that pictures could be taken. The older model had already been unloaded from the truck and driven to the designated position. After the latest model was rolled off the truck, the driver started the engine and slowly drove onto the track, toward a position next to the older model. One hundred metres short of the position, it stalled and refused to restart.

The mechanics hurried over to investigate what was causing the problem. After half an hour of heated discussion involving much bonnet lifting, hand waving, talking and pushing, it was decided that the solution to the problem would have to wait. As they pushed the car into position for the photographs to be taken, Alain, one of the photographers, nonchalantly said, "The fastest car on this track is last year’s model."
Brian, the other photographer quickly retorted, "No it's not, just last week on this track, the new model was 1.3 seconds faster per lap."
Alain then replied," You've misinterpreted what I said."
Brian snapped back, "No I haven't, you said that last year’s model is faster than the new model."
Unfortunately this is when many people will point to their opponent and say "Straw man fallacy!"

• Did Brian's evidence show that Alain's statement was false?
• Did Brian commit a straw man fallacy by misrepresenting what Alain had said?
• Are both Alain's and Brian's statements true? (We assume that Brian's information on the timing difference is correct.)

Would it make any difference if the conversation had gone along these lines?

    Alain: The fastest car on this track is last year’s model.
    Brian: I'd say you're wrong, just last week on this track; the new model was 1.3 seconds faster per lap.
    Alain: I think you've misinterpreted what I said.
    Brian: But, didn't you say that last year’s model is faster than the new model?

In this example, Brian has asked for clarification of what Alain had said, thus acknowledging that he may have misinterpreted Alain's statement. Even Brian's second statement was not a misrepresentation of what Alain had said, it was Brian's considered opinion that the new model was faster than the old model. Brian knew something which seemed to contradict Alain's statement. There was no straw man argument in this exchange. Brian did not misrepresent what Alain had said, he merely misunderstood.

____________________________________________________________________

Alain: Presently, there are two cars on the track. One was driven to its position; the other had to be pushed. Which car is faster?
____________________________________________________________________

Would it have averted any argument if Alain had included three words to his original statement? E.g., "The fastest car on this track at this moment is last year’s model."
These are the sort of errors we make each day. We often misinterpret or misunderstand other people's statements. Furthermore, we can't predict how someone might misinterpret what we are saying, so we can't include the necessary words to avoid any misinterpretation.

In the first series of comments, the sentences may have been stated in a forceful, direct and possibly accusatory manner and refuted in a defensive manner as illustrated by phrases such as; "No it's not...", "You've misinterpreted..." and "No I haven't...". Although it is implied, it is often forgotten that when each of us makes a statement it is no more than an opinion, our opinion. We may believe something is a fact, but it is only a fact in our opinion.

When we give our opinion and state it as a fact, we are in fact merely stating our opinion.

The second series makes it clearer that we are taking responsibility for the statements we are making. It may seem tautological, but at times it is important to remind ourselves that anything we say or write is just an opinion. One should always acknowledge that one may be in error.

So what is a straw man fallacy?

Here are 4 simple steps to produce a straw man fallacy.
1) Make up a statement and claim that this statement represents your opponent’s position. (In fact, this statement must misrepresent your opponent’s position)
2) Word that statement in such a manner that you can easily refute it.
3) Provide the evidence which refutes the statement that you just made up.
4) Then claim that your opponent’s position is clearly unsupportable.
(However, the 4th part is just the conclusion where you try to gloat over your brilliant rebuttal.)

One current hot topic is Anthropogenic Global Warming (AGW). With the two sides often called "Warmists" and "Sceptics". Although other terms (often derogatory) are used, for this topic I will use these terms.
A warmist wrote, “Climate sceptics deny that the climate changes”, and then gave solid evidence showing that the climate does in fact change.
A sceptic would accuse the warmist of committing a straw man fallacy.
Why? Because sceptics have always said that the climate is changing. They expect it to change in the future, as it has always done in the past; naturally. The disagreement between the two sides is whether it is humans that are causing the climate to change. The warmist has misrepresented what the sceptics claim.

In order to build an unbiased and informed opinion on any subject we must recognize these logical fallacies. But to do so we must listen to and try to understand both sides of the argument and then note any logical fallacies put forward by either side.

An easy way to avoid falling into the straw man argument yourself is to start your statement with something like: “I think my opponent believes that," (insert your interpretation here).
Then say, “If this is a true interpretation of my opponent’s position then," (insert your refutation here).
If your opponent accepts your interpretation of his position then you are not guilty of producing a straw man fallacy.
If your opponent claims that you have misrepresented his position, then you may still be guilty of producing a straw man or, as you have acknowledged, you may have honestly misunderstood or misinterpreted your opponent’s position.
This technique also engenders a sense of politeness, which is usually best.
It is important to identify whether your opponent has misrepresented, misunderstood or misinterpreted what you said, before you accuse your opponent of committing a straw man fallacy.

Because of the complexities involved in a straw man argument, it is probably one of the most commonly alleged and yet misunderstood of all logical fallacies. Other fallacies such as misrepresentation, questionable premise, quoting out of context, slanting, equivocation and smear tactic may be elements of a straw man fallacy. Misunderstanding or misinterpreting are not fallacies, however misrepresenting (lying) is a logical fallacy.

For a good explanation of some common logical fallacies try the Internet Encyclopedia of Philosophy: http://www.iep.utm.edu/fallacy/
For example:

"Straw Man
You commit the straw man fallacy whenever you attribute an easily refuted position to your opponent, one that the opponent wouldn’t endorse, and then proceed to attack the easily refuted position (the straw man) believing you have undermined the opponent’s actual position. If the misrepresentation is on purpose, then the straw man fallacy is caused by lying."

A Mythical Axiom

When someone gets charged with committing a crime, the police prosecutor believes there is sufficient evidence to arrest the suspect. The law tells us what we must not do. We are permitted to do anything, so long as it is not prohibited by the law.

The allegation is that we did something which is prohibited by law. The suspect and his lawyer must now try to prove a negative, i.e. the suspect did not commit the said offence.Those who believe that it is impossible to prove a negative are saying there's no point in denying it because, "You can't prove a negative".

So there's no point in having courts of law, judges, lawyers, jurors etc. because the suspect can't prove a negative? He can't prove that he did not commit the crime? Of course, those who assert that you can't prove a negative don't apply their generalization (their axiom) in these cases. They will argue that every suspect has the right to attempt to prove that they did not commit the crime, yet still they assert that one can't prove a negative.

They are selective as to the application of the axiom. They get around this contradiction by re-wording the case for the defence as, "The defendant may attempt to prove his innocence". That doesn't sound like a negative. So everything is ok, right? So, the axiom is not challenged.

The problem with this word manipulation is that innocent means not guilty.
"The defendant is guilty" means the same as "The defendant is not innocent".

Fortunately in law, the onus of proof remains on the prosecution at all times.

In science however, researchers write papers describing how they arrived at their conclusions. Let's imagine that a researcher has concluded that cyclones are caused by the level of carbon dioxide in the atmosphere. Other researchers are sceptical of this conclusion and must set out to prove that the level of carbon dioxide does not cause cyclones. Oh no! You cannot prove a negative. Is there any point in trying?

Fortunately in science, researchers must provide the evidence that supports their conclusions, and consider any evidence which may contradict their conclusions.

Whether a statement contains the words no or not does not mean that the statement cannot be proven or disproven. Make any statement you like, you must then be able to give evidence to support that statement.
Quod gratis asseritur, gratis negatur – What is asserted without reason (or evidence) may be denied without reason (or evidence).

Here's a statement that some consider to be a fundamental, self-evident truth (an axiom):
"You cannot prove a negative". The statement itself is a negative.
Can you prove that you cannot prove a negative?
If you can, then you have just proven a negative and contradicted your statement.
If you cannot, then the statement is not an axiom.


The statement, "The absence of evidence is not evidence of absence", is a negative.
If "You can't prove a negative" is true, then "The absence of evidence is not evidence of absence" cannot be proven to be true. Both cannot be true.

If "The absence of evidence is not evidence of absence" can be proven to be true, then "You can't prove a negative" is false.  ...{1}

1) If evidence has not been sought or is impossible to obtain then the absence of evidence is not evidence of absence. For example, I am unable to obtain evidence that life exists on Neptune's moon, Triton. This absence of evidence is not evidence of the absence of life on Triton. As such, I cannot say that there is no life on Triton. In this case, "The absence of evidence is not evidence of absence", is a true statement. Therefore, from {1} above, "You can't prove a negative" is false.

2) If evidence has been sought then the absence of evidence is evidence of absence.
For example, the Michelson-Morley experiment produced no evidence to support the idea that light requires aether to travel through, i.e., there is no evidence of aether.
"In addition, recent resonator experiments have confirmed the absence of any aether wind at the 10−17 level". That sounds like proof of a negative to me, i.e., there is no aether wind. http://en.wikipedia.org/wiki/Michelson%E2%80%93Morley_experiment

When a doctor conducts exhaustive tests for malignant cancer cells in a patient but finds the results are negative then the doctor is correct to say that there is no evidence of malignant cancer in the patient. Of course the doctor cannot conclude that the patient does not have cancer, merely that there is no evidence of cancer. So in these cases, the absence of evidence is evidence of absence.

Strangely, "The absence of evidence is not evidence of absence" is true, and "The absence of evidence is evidence of absence" is also true.
The obvious contradiction is caused by equivocation (ambiguity) over the meaning of "the absence of evidence". Both sentences are a clever play on words, however they lead to misinterpretation and misunderstanding.

I should point out that proof, is not the same as developing a mathematical proof which is an absolute truth. The meaning of proof as used in this context is the same as "Evidence sufficing or helping to establish a fact".

What one can or can't prove does not depend on whether the statement is worded as a negative. If it is true that one cannot prove a negative, then — Any statement that can be worded as a negative cannot be proven, including this statement; Any statement that can be worded as a negative cannot be proven.
Here are four more negative statements which are provable:

4 ≠ 5
Sir Isaac Newton did not watch television.
Kangaroos are not native to Japan.
I am not the smartest person in the world.

Is it even necessary to prove these statements? They are self-evident truths.


Ducks are animals.
Ducks only have two legs.
Proposition: If ducks only have two legs then ducks don't have four legs.

The negative consequent (ducks don't have four legs) is just as provable as the positive antecedent (ducks only have two legs).

Conclusion: Any animal that has four legs is not a duck.
By starting with a positive assertion (ducks only have two legs), I derived a negative consequent (ducks don't have four legs) and from those I drew a negative conclusion (Any animal that has four legs is not a duck).

2 + 2 = 4       (If n is any number other than 4, then 2 + 2 ≠ n)
5 ≠ 4
Therefore 2 + 2 ≠ 5

The good thing about proving a positive is that it disproves a whole lot of negatives. For example, by proving 2 + 2 = 4, we have proven that 2 + 2 ≠ 5 and 2 + 2 ≠ 6, etc. Proving a negative can disprove a whole bunch of positives, e.g. any animal that has four legs is not a duck.

For any generalization, or axiom, only one exception is required to disprove it.

How many times have I proven a negative?