Unit 6: Scientific Reasoning
Unlike the syllogistic arguments you explored in the last unit, which are a form of deductive argument, scientific reasoning is empirical. This means that it depends on observation and evidence, not logical principles. Although some principles of deductive reasoning do apply in science, such as the principle of contradiction, scientific arguments are often inductive, and for this reason, science often deals in confirmation and disconfirmation.
Nonetheless, there are general guidelines about what constitutes good scientific reasoning, and scientists are trained to be critical of their own inferences as well as those of others in the scientific community. In this unit, you will investigate some standard methods of scientific reasoning, some principles of confirmation and disconfirmation, as well as some techniques for identifying and reasoning about causation.
Completing this unit should take you approximately 4 hours.
- Upon successful completion of this unit, you will be able to:
- explain the hypothetico-deductive method and its implications for testing scientific hypothesis;
- explain Occam's Razor and its implications in real-world scenarios;
- explain the criteria scientists use to choose among competing hypothesis;
- discuss notions of causation, causal relations, and Mill's methods for reasoning about causation;
- explain the difference between correlation and causation;
- use visualization tools to represent causal relations; and
- explain several common fallacies when reasoning about causation, such as false cause.
6.1: The Basic Principles of Scientific Reasoning
Read these two tutorials on scientific reasoning. Science itself is almost infinitely varied, but its basic method is surprisingly simple. These tutorials will introduce you to the four components of the hypothetical-deductive method and the difference between truth and confirmation.
Watch these two videos. Pay particular attention to the discussion of the difference between the terms theory and evidence, as well as the discussion of the reasoning method called Ockham's Razor (which is also sometimes called Occam's Razor).
Read this tutorial on theory choice. In scientific practice, multiple theories will frequently be put forward to explain the same phenomena. When this happens, scientists sometimes use five criteria to guide their decisions among alternative theories.
- Consider the following prompts. Share your thoughts on the discussion forum by clicking on the link above and creating a free account, if you have not already done so. Review and respond to at least one or two other students’ posts.
- Given what you know about criteria for theory choice in science, such as predictive power, mechanism, fruitfulness, simplicity, and coherence, is there anything other than evidence that scientists use in determining whether to accept a theory? Should there be?
- Are simpler theories more likely to be true? Is Ockham’s Razor always a good rule of scientific reasoning?
6.2: The Question of Causality
6.2.1: The Basics of Causality
Read section 3,4 (p. 158-169) to investigate the complications of causality, particularly as it relates to correlation. Sometimes, two correlated events share a common cause, and sometimes correlation is merely accidental.
Complete exercises 25 and 26 to practice determining sufficient evidence for causation and determining accidental correlation. Check your answers against the answer keys on pages 232-233.
Read this tutorial, which outlines some important terminological distinctions for dealing with causation. Causation is an ideal topic to address in a course on critical thinking, because it is something we feel we understand well in our everyday lives. Once we begin trying to think scientifically about causes, however, we find that fixing the causes of some event requires precision and subtlety.
6.2.2: Five Ways to Identify a Cause
Read this tutorial about Mill’s five methods for identifying causes. John Stuart Mill (1806-1873), the 19th-century English philosopher, proposed five distinct ways in which a cause might be identified through observation. While these methods may appear to be close to common sense, it is important to see that they represent distinct modes of inference.
6.2.3: Causality is More Than Just Cause and Effect
Read this tutorial on causality, which identifies seven different types of causal relations. Each type of relation is followed by a set of defining criteria. Although each type of relation is a cause-and-effect relationship between A and B, information about the context of the interaction and the relation of A and B to one another in time affects what we can say about the causal relation between them.
6.2.4: The Difference Between Causation and Correlation
Read this example-rich tutorial, which explains the difference between the two relationships of correlation and causation. Scientists looking for cause-and-effect relationships in the natural world need to be careful not to misconstrue causality with mere correlation.
6.2.5: Ways of Representing Cause and Effect
Read this tutorial, which illustrates two ways of diagramming cause-and-effect. They allow for the description of multiple causes and effects from a single event as well as for distinguishing between levels of causation.
When multiple relations of cause and effect are involved in the behavior of some phenomenon, representing these relations visually is often the best way to get a handle on them and to assist in quantitative analysis of the system in question.
6.2.6: Fallacies About Causation
The following passage is an extract from a report by Arizona Daily Wildcat (June 16, 1999) concerning a study to show that certain people can communicate with the dead. Using what you have learned about causation, correlation, and causal fallacies, consider the potential flaws with the experiment. Assume that the report is mostly correct. Summarize your evaluation of the flaws in the experiment, and share your thoughts on the discussion forum by clicking on the link above and creating a free account, if you have not already done so. Review and respond to at least one or two other students’ posts.
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Gary Schwartz, psychology professor and co-founder of the University of Arizona Human Energy Systems Lab, speaks about his work at the University of Arizona. A team of scientists and students conducted a unique experiment this weekend, probing the possibility of an afterlife by studying how mediums commune with the dead.
Researchers invited a panel of mediums to meet with 10 people whose loved ones had recently died. While under observation, the mediums tried to receive information from the deceased without prior knowledge about the deceased. Schwartz invited four mediums to participate in the study, including famous "superstars" of the psychic world, such as author John Edwards, and unknowns, such as California housewife Laurie Campbell. The medium sat facing a wall while a researcher looked on. A "sitter," who had recently lost a relative or friend, would then enter the room and sit six feet behind the medium. Schwartz acknowledged that a few of the sitters were acquaintances of the mediums.
For up to 10 minutes, the medium and the sitter would sit in silence. The medium, who could not see the sitter, would concentrate on receiving psychic impressions. A question and answer session followed, in which the sitter was allowed only to answer "yes" or "no." Schwartz said the study was set up to minimize communication between the medium and the sitter, avoiding conscious or subconscious prompting between the two. While the final results have not been written up, Schwartz said he was impressed with the mediums’ performance. He said that on several occasions the mediums were able to pick out the names and personal information of the deceased.