House Warming | Chest Pains | Malaria | Turkey | Practice Exercise
This page has several examples of abduciton outlines like you will be asked to provide for homework. The practice exercise is from Dr. Lloyd Carr.
The first example will consider the initial observation that the house is warming up.
Three theories will be proposed (remember this is an example):
- The heater is on and heating the house. (A1)
- The sun is shining and heating the house. (A2)
- The roof is on fire and heating the house. (A3)
For these simple examples, assume that at least half of the criteria for a scientific theory, as previously presented, have been met. The preliminary conditions are then satisfied since any one of these conditions could cause the house to become warmer.
The following data will be assumed true for this example (these would come from information about the day when the initial observation was made):
- There is no smoke from the roof. (D1)
- It is cold outside. (D2)
- It is raining hard outside. (D3)
A table that shows when a theory leads us to expect a specific piece of data can now be constructed. A "yes" means that the data is expected or very probable given that theory; If A were true, then it would lead us to expect D. For example, the "yes" in the upper left box results when the theory that the heater is warming the house leads us to expect the observation that there is no smoke coming from the roof. Since a heater would not cause smoke to come from the roof, the theory does make the observation highly probable. The same could be said for the sun shining. If the roof was on fire, however, you would expect some smoke from the roof and so the third theory does not make the observation likely that no smoke is coming from the roof. That is why there is a "no" in the intersecting box. This same process is done for each box. If a theory says nothing about a piece of data, place a "no" in the box.
Heater Sun Fire No Smoke yes yes no Cold Outside yes no no Raining Hard no no no
Given this data, the heater theory leads us to expect more of the observations than either of the other two theories and will be the "best" theory; it will be the most probable explanation of the house's warming up compared to the alternatives being considered. Notice that the observation that it is raining hard outside doesn't differentiate the theories and, indeed, it could be eliminated. Also, remember that the process is a process of elimination and not a process of "proving a theory to be true." Even though the heater theory is the best alternative given these theories and this data, there is still a chance that it is not the true explanation for the house's warming up.
The second example will consider the initial observation that a person has chest pains.
Two theories will be proposed in this example:
- The person is having a heart attack. (A1)
- The person is having a gall bladder attack. (A2)
Again assume that at least half of the criteria for a scientific theory, as previously presented, have been met. The preliminary conditions are then satisfied since either of these conditions could cause the person to have chest pains.
The following data will be assumed true for this example (these would come from information about the person when the initial observation was made or when subsequent observations are made):
- The person has an erratic EKG. (D1)
- The person takes high blood pressure medication. (D2)
- The person has high blood levels of an indicator for heart attack. (D3)
A table can now be constructed by determining whether or not the conditional "If A were true, then it would lead us to expect D" is satisfied for all combinations of theories and data. A "yes" means that the conditional is satisfied and the theory lead us to expect the observation.
Heart Gall Bladder Erratic EKG yes yes Blood Pressure Meds yes no High Heart Attack Indicator yes no
Given this data, the heart attack theory leads us to expect more observations and will be the "best" theory; it will be the more probable explanation for the chest pains compared to the alternative being considered.
The third example is from the 29 April 2006 edition of the magazine Science News (Vol. 169, No. 17, P. 260). They state that only a small percentage of mosquitoes that could infect people with malaria in Africa carry the malaria parasite. This led scientists to suspect a genetic link for warding off malaria. They narrowed the DNA markers to two possibilities called APL1 and APL2.
A genetic marker is responsible for warding off malaria.
Two theories will be proposed in this example:
- APL1 is responsible for warding off malaria. (A1)
- APL2 is responsible for warding off malaria. (A2)
Again assume that at least half of the criteria for a scientific theory, as previously presented, have been met. Either of these genetic markers could be responsible for the effect. The preliminary conditions are then satisfied.
Experiments were performed with the following results:
- Turning off APL1 (and leaving on APL2) increased the malaria indicators 10-fold. (D1)
- Turning off APL2 (and leaving on APL1) didn't change the malaria indicators. (D2)
A table can now be constructed by determining whether or not the conditional "If A were true, then it would lead us to expect D" is satisfied for all combinations of theories and data. A "yes" means that the conditional is satisfied and the theory lead us to expect the observation.
APL1 APL2 APL1 Off yes no APL2 Off yes no
Given this data, the theory that APL1 is responsible for warding off malaria leads us to expect more observations and will be the "best" theory; it will be the more probable explanation for protection from malaria compared to the alternative being considered.
People feel especially drowsy after a big turkey dinner.
There were two theories posed to explain why we get especially drowsy after a big turkey dinner:A1: Tryptophan. Turkey contains tryptophan which scientific studies have shown to affect sleep and mood.
A2: Digesting food. After eating a large meal the body is using energy to digest food which makes us drowsy.
Assume both of these theories have merit, satisfying at least half of the criteria for a scientific theory (it will be required to show this later). Also, both theories could explain the initial observation (as described above).
D1: Turkey does not contain an exceptional amount of tryptophan. Chicken and beef contain about the same amount, and pork and cheese contain more tryptophan per gram than turkey. This also suggests that eating other foods would make us the same or more drowsy than eating turkey.
D2: Turkey is most often eaten during holidays with lots of other food. When turkey is consumed with other foods, absorption of tryptophan from turkey is minimal.
D3: Some scientists suggest that everyone feels drowsy after eating a large meal because the body is using energy to digest food and blood flow and oxygenation to the brain decreases.
Tryptophan Digesting food D1 no no D2 no no D3 no yes
From this data (Tryptophan - 0, Digesting food - 1), it would seem that digesting food best explains why we get drowsy after eating a large turkey dinner.
Here is a case of abduction based on a real event. A person buys an expensive bush to make the yard look good. He plants it and it thrives over the summer but does not survive the winter, come spring it's dead. The nursery will replace it, but the person wants to find out what killed it so that the next one can be protected properly. The nursery experts suggest two possible causes, each equally likely that particular year: (a) the bush was planted in a spot that exposed it to too much cold, specifically deep frost killed the roots before they were sufficiently established; (b) grubs from a beetle attacked the roots during winter and killed it. Knowing the correct explanation would allow the homeowner to take the right action when planting the replacement, the nursery experts said to dig up the dead bush carefully and examine the roots. If grubs killed the bush, then the dirt around the roots should contain numerous signs of larvae. But if frost killed the bush, there should be no signs of larvae for they only live below the hard freezing line. On the other hand, if frost killed the bush, then the roots should be soft and spongy and easy to break; but if it wasn't frost, the roots should be firm and flexible. The person dug up the dead bush as instructed and found the roots all soft and spongy, and no signs of larvae in the soil. The new bush was planted in a more sunny and protected part of the yard.
Use the ideas of abduction to organize this information as shown in the preceding examples. After you have written your answer down, you can compare it to this abduction outline.