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Module 14: Evaluating Arguments - Inference to the Best Explanation – Spring 2026

Critical Thinking Online

Fayetteville State University

Dr. Jon Young, Instructor

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Learning Outcomes: In this lesson, you will..

Recall the distinction between arguments and explanations.

Identify in specific examples the state of affairs or phenomenon that an explanation seeks to explain.

Distinguish theoretical explanations (the focus of this lesson) from procedural, interpretive, and teleological explanations.

Explain how the pattern of reasoning known as “inference to the best explanation,” makes an argument whose conclusion claims that one explanation or theory is better than others.

Apply the minimum criteria of consistency in evaluating specific theories.

Explain each of the five criteria of adequacy: testability, fruitfulness, simplicity, scope, and conservativism.

Apply the criteria of adequacy to specific examples.

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Assignments & Assessments: You will:

Complete the Required Readings

PowerPoint Introduction

Chapter 11.1 – 11.3 in your electronic textbook .

Earn at least 6 of 10 points on the Quiz.

Submit a writing assignment.

Contribute to the Discussion.

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Critical Thinking

Remember our definition of critical thinking – the systematic evaluation and formulation of belief, or statements, by rational standards. Since midterm we have been identifying and applying deductive and inductive argument patterns to becoming more systematic in our application of rational standards.

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Fourth Inductive Argument Pattern

This week we examine our fourth pattern of inductive arguments: Inference to the best explanation.

It is important to keep in mind that this argument IS inductive. The premises are NOT intended to guarantee the truth of the conclusion, but instead are intended to establish the truth of the conclusion with some degree of probability (ranging from a little more likely true than false to nearly certain.)

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Inference to the best explanation

Inference to the best explanation is an argument whose conclusion is that one explanation is better than others.

This week you will learn methods and criteria for concluding that one explanation is best because it is most likely true based on current evidence. (New evidence may change our assessment of other possible explanations.)

The primary focus this week will be the five criteria of adequacy (testability, fruitfulness, simplicity, scope, and conservatism) and the TEST formula of evaluating alternative explanations.

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Remember: Arguments vs. Explanations

As we learned at the beginning of the semester, an argument gives reasons for believing that something is the case while an explanation seeks to give an account of why or how something is, was, or will be.

An argument has a conclusion supported by reasons for accepting the conclusion. The truth of the conclusion IS in question. (That’s the purpose of an argument: to establish the truth of the conclusion.)

An explanation begins with a phenomenon, or state of affairs, that is NOT in question, and gives an account of how it came to be.

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Inference to the best explanation

Sometimes, one explanation is sufficient. If I wake up to frozen water on my driveway, I can explain this state of affairs by saying the temperature dropped below freezing last night.

But what happens when we have several reasonable, viable explanations for a phenomenon? For example, researchers are still trying to determine the origins of Covid 19. That we had a worldwide pandemic that killed millions is NOT in question, but at least three competing theories have been offered for its origin: 1) transmission from infected animals in a meat market in China; 2) that it was accidentally leaked from a laboratory in China where the SARS virus was being studied. More about these competing explanations below.

Inference to the best explanation is argument whose conclusion is that one of these explanation is the best.

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Criteria of Adequacy for good explanations Make flash cards for these five terms

Testability – A good explanation if testable; lends itself to confirmation (or disconfirmation); there is a way to determine whether it is true of false;

Fruitfulness – A good explanation yields unanticipated insights discoveries about other phenomena beyond the one being explained. (more applicable to scientific theories than everyday explanations)

Scope – A good explanation accounts for more than the current phenomenon; it accounts for a variety of associated facts and phenomena.

Simplicity – A good explanation does not require assumptions that raise more questions than answers.

Conservatism – A good explanation is consistent with existing knowledge.

(The funny student started crying. This is my mnemonic device. Perhaps you can devise a better one.)

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Common Sense example – Car Won’t Start. Why?

Criteria	1. Battery is dead	2. Car out of gas	3. Inhabited by ghost
Testability	Replace the battery and see if it starts	Check the gas gauge	No way to confirm
Fruitfulness	Could explain why other cars won’t start	Could explain why other cars won’t start	Applies to this car only
Scope	Explains why lights and radio will not come on	Explains only the car not starting	Difficult to determine
Simplicity	Requires no additional assumptions	Requires no additional assumptions	Requires assumption that ghosts exist and occasionally inhabit cars.
Conservatism	Consistent with existing knowledge	Consistent with existing knowledge	Is inconsistent with existing knowledge

The ease of testing 1 and 2 make this a simple example. The scope of 1 makes it superior to 2.

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Moon Landing – July 1969

Criteria	1. Actually Occurred	2 A hoax – filmed in movie studio
Testability	Many people observed rockets taking off, saw the spacecraft return to earth	Consider film technology at the time: could image from moon be faked? Yes.
Fruitfulness	Subsequent missions make more sense if first trip was real.	Purveyors of the hoax would have to argue that all moon landings were hoaxes.
Scope	Consistent with many different facts: testimony of astronauts, observers; rocks from moon unlike earth. (The rippling of the flag can be explained by momentum of turning the flag pole.)	This explanation points to the rippling of the American flag when it is planted: with no atmosphere, the flag should not ripple. Leaves much else unexplained
Simplicity	Requires no additional assumptions	Requires us to assume that millions of people could participate in hoax and no one “spills the beans”
Conservatism	Consistent with existing knowledge	Inconsistent with too much other evidence
The explanation that the moon landing actually occurred meets more of the criteria and so is very probably true.

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Case Studies

The best way to understand Inference to the Best Explanation is to consider real-life examples.

The next slides offer three case studies that apply the criteria to proposed explanations about phenomena that will likely remain unresolved until further evidence is uncovered (and the needed evidence may never be found): Malaysia flight 370 (the flight that disappeared) and the origins of Covid 19.

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Case Study 1: Malaysia Flight 370: The Flight that Disappeared

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Important NOTE:

As I am working on this lesson (December 12, 2025) a new search for the wreckage of Malaysia Flight 370 (MH 370) has been announced to begin on December 30. The new search will be aided by more adance technology than previously available for scanning the ocean floor. The search is to last 55 days. So, there is a strong possibility that by the time we get to this lesson, the mystery of MH 370 will finally be resolved.

The disappearance of MH 370 is tailor-made for conspiracy theorists; if you do an internet search, you will find many of them. It will be interesting to see if the new information silences the conspiracy theorists.

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Basic Information – Malaysia Flight 370 (MH 370)

Departed from Kuala Lampur in Malaysia at 12:42 am on March 8, 2014 – Destination was Beijing, China

Zaharia Ahmad Shah (53) Senior Pilot; Fariq Hamid (27) First Officer – the last flight required before earning full certification as pilot

10 flight attendants; 227 passengers

Radio contacts between plane and traffic control at 1:01 am (@ 20 minutes into the flight) and at 1:12 am (@ 30 minutes into flight)

1:21 am MH 370 drops off radar – never to be heard from again

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Basic Information – Malaysia Flight 370 (MH 370)

6:32 am (about the time the plane should have been landing in Beijing) emergency response initiated – should have been much earlier, but there was miscommunication between the Malaysian and Vietnamese air traffic control.

Search for plane involved 34 ships and 28 aircraft from seven different countries, continued for approximately two months

Plane has never been found, though debris has been found in distant locations in the Indian Ocean.

Note: NBC show Manifest (plane disappears for five years) Show’s creator originally tried to get the show on the air 10 years ago, networks were not interested, but after MH 370, the show was produced.

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How to explain?

Remember definition of explanation – gives an account of why or how an event occurred. The focus of the explanation is not question. In this case, MH 370 disappeared – that is not in question.

Most airplane crashes occur as a result of human error, mechanical failure, or sometimes intentional suicide by a pilot; or (in case of 9/11 attacks) hijacking.

Other facts emerged in following months

Reconstructed radar information from various sources has emerged.

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Anticipated flight path of MH 370

Kaula Lampur to Beijing

@6 hours

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Actual flight path

The plane flew for approximately six hours, but in wrong direction.

Radar shows -flew Toward Beijing, but then turned back and flew over Malaysia, then around Indonesia, and the made very steep descent into Indian Ocean too steep to have been an attempted ocean landing. Debris from the plan (July 2015) has been found in Indian Ocean.

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Debris from the flight has been found in very distant places.

Original flight plan

Debris found as far away as these locations.

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Many theories (Time Warp, Black Hole)

None of the following (usual causes) is consistent with flight plan: Computer glitch, control-system collapse, squall lines, ice, lightning strike, bird strike, meteorite, volcanic ash, mechanical failure, sensor failure, instrument failure, radio failure, electrical failure, fire, smoke, explosive decompression, cargo explosion, pilot confusion, medical emergency, bomb, or war

One explanation is that the Russian government stole the plane as a way of diverting attention away from their annexation of Crimea which was occurring at the time. In fact, (according to this theory) the plane landed in Kazakhstan. Evaluate by criteria of adequacy:

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Apply Criteria of Adequacy to “Russian Theory”

Criteria	Yes/No	Explain
Testable? Is it possible to confirm truth?	Yes	Find the airplane in Kazakhstan
Fruitfulness? Does it provide basis for novel predictions?	Yes	Predict that Russia may engage in deception for their own political benefit.
Scope: How many phenomena does it explain?	No	Does not explain actual flight path not debris in Indian Ocean
Simplicity – Number of assumptions required. (the fewer the better)	No	Plane’s equipment programmed to give false data; debris from plane was planted. (raises more questions than answers)
Conservatism – How much does it fit with existing knowledge.	Yes	We know that Russia engages in deception frequently; it seems like something Russa would do, but that does not answer all the questions raised about simplicity and scope.

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Best Explanation

The flight path can only be explained if one of the pilots intentionally diverted the plane from its original flight plan. Most experts who have studied the flight path suggest that the sharp turns would have requirement manual (not auto) pilot. Moreover, the time of turn was at a moment when flight transitioned from Malaysian to Vietnamese ground control, when its disappearance might more easily be overlooked.

Plane flew from altitude of 35,000 feet to 40,000 feet – plane was depressurized so all the passengers would have died for lack of oxygen (the masks that fall down are good for only about 15 minutes) Pilots have masks that can be used for many hours.

All communication systems were shut off manually.

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Intentional Action by Pilot

Which pilot? Senior Pilot, Shah Zaharia Ahmad Shah (53) or Fariq Hamid (27)

More likely the older pilot: he was separated from his wife, children were grown – admitted to others that he was lonely; he had set up flight simulator which he used quite a bit, and simulated the flight plan that the MH 370 took.

Is it likely that a pilot would kill his passengers and flight crew to commit suicide? This seems unlikely, but (though rare) there are some precedents.

1997 a pilot from Singapore – plunged Boeing 737 into a river at supersonic speed.

1999 Egyptian airline intentionally crashed off of coast of Long Island.

2013 – Mozambique airline deliberately crashed.

2015 (after MH 370) the co-pilot of German flight locked the pilot out of cockpit when he went to bathroom and then crashed plane into French Alps. (discovered that the pilot had studied MH 370)

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Apply Criteria of Adequacy to “Pilot Action”

Criteria	Yes/No	Explain
Testable? Is it possible to confirm truth?	Yes	Find the plane’s black box – (not likely)
Fruitfulness? Does it provide basis for novel predictions?	Yes	Suggests the need for more careful study of pilot’s mental health
Scope: How many phenomena does it explain?	Yes	Deviation from original flight plan, communication system shut down, debris; crashing the plane in expansive Indican Ocean would make it more difficult to find debris and the black box than in much smaller China Sea.
Simplicity – Number of assumptions required.	Yes	Doesn’t require any unnecessary assumptions
Conservatism – How much does it fit with existing knowledge.	Yes	Pilot depressed; Other examples of pilots who have crashed their planes to commit suicide.

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Based on Criteria of Adequacy

Pilot action is the best explanation because it meets most fully the criteria of adequacy. This does not mean we can be certain that it is true, but just that it is the best option of the alternatives offered so far. With additional evidence, another explanation may emerge as best.

If the “black box” or the wreckage of MH 370 is ever recovered, it will provide new evidence that could potentially suggest another explanation.

Unfortunately, it is very, very unlikely that the black box will be found or even that the wreckage will be recovered.

If you are interested in this subject, I recommend that you watch the 3-part Netflix series “MH 370: The Flight that Disappeared.” (2023) It offers three theories (two of which seem like conspiracy theories) for the plane’s disappearance. The Netflix series dismisses the pilot action theory, but does not offer a better alternative.

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Case Study 2: The Origins of Covid 19

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The Origins of Covid 19

That Covid 19 occurred is NOT in question. We all witnessed its spread and the sickness and death that resulted from it.

Yet, why or how it occurred remains a mystery. Two proposed explanations have emerged. Without new evidence it may be impossile to determine the origins of Covid 19.

The following slides are excerpts from a New York Times article of June 14, 2024.

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Dueling theories

The origin of the Covid virus remains the pandemic’s biggest mystery. Did the virus jump to human beings from animals being sold at a food market in Wuhan, China? Or did the virus leak from a laboratory in Wuhan?

U.S. officials remain divided. The F.B.I. and the Department of Energy each concluded that a lab leak was the more likely cause. The National Intelligence Council and some other agencies believe that animal-to-human transmission is more likely. The C.I.A. has not taken a position. The question remains important partly because it can inform the strategies to reduce the chances of another horrific pandemic.

A recent Times Opinion essay — by Alina Chan, a biologist — refocused attention on the issue by making the case for the lab-leak theory. In today’s newsletter, I’ll try to lay out the clearest arguments for each side to help you decide which you consider more likely.

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The case for natural transmission

1. It’s the norm.

Covid is part of the coronavirus family, so named because the virus contains a protein shaped like a spike. (Corona is the Latin word for crown.) In recent decades, the main way that coronaviruses have infected people is through animal-to-human transmission, which is also known as natural transmission.

The SARS virus, for example, appears to have jumped from civet cats, a relative of the mongoose, to humans in Asia in 2002. MERS seems to have jumped from camels to people in the Middle East around 2012. There is no previous example of a major coronavirus escaping a lab.

When you’re trying to choose between a historically common explanation for a phenomenon and an unusual explanation, the common one is usually the better bet.

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. Look around the market.

Two scientific papers have pointed out that a suspiciously large number of early confirmed Covid cases had connections to the Huanan Seafood Wholesale Market in Wuhan. Many of these cases, in late 2019, occurred in people who lived near the market. This map comes from a Times story about the research

Importantly, the market also sold live animals, including raccoon dogs, that scientists previously found to be susceptible to coronaviruses.

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3. Look inside the market.

Shortly after Covid began spreading, Chinese scientists swabbed walls, floors and other surfaces inside the Huanan market for the virus. They found a cluster of positive samples in the market’s southwest corner, where 10 stalls sold live animals.

“Strikingly, five of the samples came from a single stall,” my colleagues Carl Zimmer and Benjamin M

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The case for a lab leak

1. Follow the lab.

If historical logic points to natural transmission, a different concept arguably points to a lab leak: Occam’s razor. It’s a philosophical principle holding that the simplest explanation for a phenomenon is usually the correct one. In this case, a new SARS-like virus started in a city with one of the world’s leading labs for researching SARS-like viruses. Many Chinese cities have markets selling live animals; only one is home to the Wuhan Institute of Virology.

The Wuhan lab maintained “one of the world’s largest repositories of bat samples, which has enabled its coronavirus research,” U.S. intelligence officials have written. Before the pandemic, the lab’s scientists traveled to faraway caves to collect virus samples. And bats, like raccoon dogs, can carry coronaviruses.

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One possibility is that a virus that would otherwise have remained in the caves infected a lab employee. Another possibility is that scientists in Wuhan engineered a contagious new virus while researching cures and that the virus accidentally escaped.

2. Leaks happen.

In recent decades, reports suggests that laboratory employees working on a variety of diseases have been accidentally infected in the United States, Britain, China, Germany, Russia, South Korea and elsewhere.

Even before the pandemic, the Wuhan lab seemed to present a safety risk. When one outside expert heard that the lab planned to research coronaviruses without using state-of-the-art precautions, he wrote in 2018 that “U.S. researchers will likely freak out.”

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3. China controls the evidence.

It’s worth asking which of the two stories China would rather the world believe. Either would be damaging, but a lab leak seems significantly more so. It would mean that China’s scientific incompetence killed millions of people — which could explain why Chinese officials have worked so hard to restrict outside research and scrutiny about the virus’s origins.

The bottom line

Do you find both explanations plausible? I do.

As I’ve followed this debate over the past few years, I have gone back and forth about which is more likely. Today, I’m close to 50-50. I have heard similar sentiments from some experts.

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Criteria of Adequacy

If we apply the criteria of adequacy to both proposed explanation, we will see why it is impossible – without further evidence that China has yet to share – to determine that one explanation is better than the other.

Explanation 1: Natural Transmission – from live animal sold at Wuhan Seafood Market.

Explanation 2: Lab Leak – Wuhan Institute of Virology hold many species of bats which are often carriers of viruses.

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Natural Transmission Criteria	Yes/No	Explain
Testable? Is it possible to confirm truth?	Yes	Concentration of early cases of Covid 19 were near Wuhan Seafood Market; virus was found in stalls where live animals were sold. Some of these live animals could have been infected.
Fruitfulness? Does it provide basis for novel predictions?	Yes	Suggests the need for more careful monitoring of sale of live animals.
Scope: How many phenomena does it explain?	Yes	No existing evidence contradicts this explanation. But we do not have an evidence of infected animals, nor or animal traders being infected, or spread of virus from the market. China controls this evidence and has not been willing to share it.
Simplicity – Number of assumptions required.	Yes	Doesn’t require unnecessary assumptions;
Conservatism – How much does it fit with existing knowledge.	Yes	Natural transmission is the normal way diseases are spread; so thisexplanation is consistent with existing knowledge.

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Lab Leak - Wuhan Institute of Viroloty - Criteria	Yes/No	Explain
Testable? Is it possible to confirm truth?	Yes	Consistent with concentration of early cases – near the Institute of Virology; housed many species of bats; an employee could have een infected by bats
Fruitfulness? Does it provide basis for novel predictions?	Yes	Suggests the need for more careful safety procedures to prevent future deadly lab leaks.
Scope: How many phenomena does it explain?	Yes	No existing evidence contradicts this explanation. But we do not have an evidence of infected animals, nor or animal traders being infected, or spread of virus from the market. China controls this evidence and has not been willing to whare it.
Simplicity – Number of assumptions required.	Yes	Doesn’t require unnecessary assumptions;
Conservatism – How much does it fit with existing knowledge.	Yes	It is not uncommon for lab employees to become infected and spread a disease; reports in U.S. Britain, China, Germany, Russia, and Southe Korea

The Origins of Covid 19

We have two equally plausible explanations – we cannot say that one conforms to the criteria of adequacy more than the other. If China were to share some of the missing evidence, we could possibly resolve the issue, but it does not seem that China will share this information either because they do not have it or they have it but fear it would make them look bad.

(Unfortunately, as with so many other current issues, the origins of Covid 19 have been politicized based on different group’s views about China. (Those who distrust China are quick to jump on the lab lead theory. When Donald Trump suggested the lab leak theory, many liberals said it could not be true if Trump believe it. Please, my dear students, If you take nothing else away from this course, please remember this: do not let politics distort your review of evidence.)

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Case Study#3: Death of Gene Hackman and wife Nancy Arakawa

“Sheriff: Gene Hackman, wife found dead in Santa Fe home; no foul play suspected” Headline in Santa Fe New Mexican, Feb. 27, 2025

The award-winning actor, Gene Hackman (95), and his wife, Nancy Arakawa (65), had lived for many years in Santa Fe, New Mexico (where I now live). So it was especially shocking here when the news was reported that the pair were found dead. Their bodies were found in separate rooms. One of their three dogs was also found dead. Hackman’s body was found in a mud room near a door; a cane and pair of sunglasses were near his body. Arakawa’s body was found in a bathroom in a different part of the house. One of their three dogs was also found near her body.

The immediate question: How to explain? The phenomenon (event, state of affair to be explained was these deaths. There is no question the two have died – the task is to give an account of how or why the deaths occurred.

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Initial Speculation

When a celebrity is found dead under unusual circumstances, you can expect much speculation to circulate on social media. Since there was no evidence of either bing shot, stabbed, or assaulted, some suggested poisoning, possibly by a visitor, or perhaps one gave poison to the other and then ingested it him/herself as part of a suicide pact.

Carbon monoxide poisoning became the most widely-accepted first explanation. (Everyone I knew accepted this explanation. This explanation fits the criteria of adequacy. It has scope, explaining the different location of he bodies. It is simple, requiring no questionable assumptions; conservative, as it is consistent with what we know about the lethal effects of carbon monoxide; and it is fruitful in that it can also explain other deaths under similar circumstances.

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Final Explanation

Carbon monoxide poisoning is also testable and none of the examinations of the house or the bodies showed any traces of carbon monoxide.

Further investigation found that Hackman had been dead for @ nine days (based on activity of his pacemaker) and Arakawa had been dead for longer, a victim of the hantavirus. Since she was the primary caretaker of Gene Hackman, who also suffered from Alzheimer’s disease, he probably was unable to take care of himself and finally died.

Hantavirus is virus carried by mice and the couple lived in secluded, wooded area that are often infested with mice.

This explanation meets all five of the criteria of adequacy and so is the one that has been accepted. (Of course, it’s possible, though not likely, that new evidence will emerge, that would alter this explanation.)

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Postscript

As I am working on this lesson (December 15, 2025), I just read that the jury has found Brian Walshe guilty of first-degree murder of his wife. Several months will have passed by the time you read this lesson. Brian Walshe is the man who confessed to dismembering and disposing of his wife’s body, but he denied murdering her. He claimed that when he found her dead, he panicked and took the actions he took. Evidently, the jury did not accept that explanation. It seems to me the most relevant criteria in this case is simplicity. That Walshe intentionally murdered his wife and then disposed of her body requires no questionable assumptions, while his explanation requires us to assume that one way a person might react to the discovery of a dead person is not to call an ambulance or law enforcement , but to take several trips to the hardware store to buy the tools needed to dismember her body and clean up afterwards. How many people do you know who would react in such a manner. The first-degree murder is also consistent with what we know about murder: unfortunately, all too often when a person is murdered, it turns out the cuprit was the person’s spouse or partner.

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Read Ch.11.1 -11.3 in your electronic textbook .

Earn at least 6 of 10 points on the quiz.

Submit a writing assignment.

Contribute to the Discussion.

Good luck!!

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