Download Inductive and Deductive Reasoning

Scientific Reasoning
In both lines of scientific work—empirical and theoretical—we can describe the sequence of
work as a create-test-use (CTU) process.
 Create the empirical or theoretical concept/hypothesis, inductively.
 Test the empirical or theoretical concept/hypothesis.
 Use the empirical or theoretical concept/hypothesis, deductively.
This CTU process also describes the different scientific purposes of scientific work. At any one
time, some scientists are creating new empirical or theoretical concepts, some are testing
current concepts to determine its limits, and some are using accepted concepts to add to the
knowledge base and solve practical problems. The following section and exercise is restricted to
discussing create (inductive) and use (deductive) reasoning.
Inductive and Deductive Reasoning
Greek “science” was not really science in the modern sense because it involved no
experimentation. Instead the Greeks developed knowledge by logically arguing from a set of
assumed concepts such as Aristotle’s theory of matter as composed of four elements—earth, air,
fire and water. The initial premise or proposition was established and accepted simply based on
authority, not evidence. However, once the initial concept is accepted, specific conclusions can
be deduced by logical arguments. This method of reasoning from the general to the specific is
the method of deduction. In modern science, once an empirical or theoretical concept becomes
widely accepted within the scientific community, deductive reasoning is necessary to use the
concept in various applications.
Traditionally, the view of science is as a process of collecting many objective (unbiased)
observations with the aim of creating general patterns. This view, as expressed by Sir Francis
Bacon in 1620, is the method of induction—reasoning from the specific to the general. Although
this method appears to be a useful description of the early days of modern science when
comparatively few empirical and theoretical concepts existed, it is not a method that is generally
used by scientists today. Nevertheless, it is still widely used in the teaching and learning of
science—as history is re-enacted.
Exercise
1.
A student-group tests the properties of elements on the left side a modern periodic table in
the laboratory. They find that these elements conduct electricity and are shiny and
bendable. They write an empirical definition of these elements that we now call metals.
The type of scientific reasoning that they are employing is
A. inductive reasoning
B. deductive reasoning
C. reasoning from the general to the specific
D. reasoning that uses a concept
Answer: A The reasoning was from the specific to the general—creating an empirical
definition for metals.
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2.
A student group in a laboratory setting are given the task of determining the resistance of
several resistors, without using an ohmmeter. The measure the current through the
individual resistors and the voltage drop over the same resistor in a simple electrical circuit.
They then calculate the resistance from Ohm’s law (I = V/R or R = V/I). The type of
reasoning that they are employing is
A. inductive reasoning
B. deductive reasoning
C. reasoning from the specific to the general
D. reasoning that creates a concept
Answer: B The reasoning was from the general to the specific—using Ohm’s law to
calculate the resistance of the resistors.
3.
Inductive and deductive reasoning are pervasive in science, in science education, and in
everyday life. For example, scientists and science students use concepts (e.g., F = ma)
deductively everyday to calculate an unknown from a given number of variables (e.g., m).
Classify the following reasoning as inductive or deductive.
a. anecdotal evidence is used to generalize that eating candy creates misbehaviour
b. misbehaviour of a specific child is blamed on the eating of candy
c. a prediction is made from an hypothesis
d. evidence is analyzed to create a hypothesis
e. knowledge of experimental designs is used to evaluate a specific design
Answer: inductive; deductive; deductive; inductive; deductive
4.
Students often confuse interpretations and observations. One description is that
observations are recorded in the Evidence section of a laboratory report, while
interpretations of the observations are made in the later Analysis section of a laboratory
report. Interpretations may be inductive or deductive; i.e., an interpretation can create a
concept from observations inductively, or an interpretation can use a concept, deductively.
Classify the following as an observation, an inductive interpretation, or a deductive
interpretation.
a. This rock is not alive.
b. This rock does not grow.
c. Rocks do not grow.
Answer: deductive interpretation, observation, inductive interpretation (Of course, one can
argue about the interpretation of the word “grow”.)
Use the following information to answer questions 5 and 6.
The planet Neptune was observed by Galileo in 1613 and also by later astronomers without
being recognized as a planet. About two hundred years later, another astronomer, named Le
Verrier, predicted (based upon Newton’s law of universal gravitation) the existence of
Neptune to account for the orbit of Uranus. Le Verrier predicted the mass, diameter, and
calculated the orbit of Neptune. Within a very short time, several astronomers discovered
the new planet as predicted.
5.
The prediction of Neptune by Le Verrier is an example of
A. inductive reasoning
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B. deductive reasoning
C. a theoretical hypothesis
D. none of the above
Answer: B (Newton’s law of universal gravitation was employed deductively to make the
prediction.)
6.
Why is Galileo not credited with the discovery of Neptune? What does this illustrate about
the nature of science?
Answer:
Galileo did not interpret his observation as being a planet. This illustrates that having the
concept allows you to interpret an observation, deductively.
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