Critical Evaluation Toolkit

Developing students' reasoning skills

To make informed judgements, evaluations and analyses, students must know some basic principles of reasoning. A grasp of logic helps to examine the validity of assumptions and opinions. Some basic terms associated with logic and reasoning are:

Inductive reasoning: starts from specific facts or observations to arrive at a general conclusion (e.g., When I stay in the sun too long, I get sunburnt, so if I go to the beach this summer I will get sunburnt). Inductive reasoning relies on evidence, which must be accurate, complete, relevant and adequate to prove the point.

Deductive reasoning: makes a general observation and works back to a specific example (e.g., All lengthy exposure to the sun leads to sunburn; I am exposed to the sun for long periods...; Therefore I will get sunburnt). Deductive reasoning relies on rules of inference. The difference between deductive and inductive reasoning is in the form in which the argument is expressed - deductive logic works according to a tightly prescribed syllogistic form; inductive logic is 'looser.'

Syllogism: a construction such as the one above, in which the various parts (premises and terms), have precise functions within a consistent schema.

Argument: a rhetorical device in which a claim or proposition is proved by the use of evidence or inference. Argument differs from 'persuasion', in that it does not rely on strategies that affect the emotions.

Assumption: a belief, that the person making the argument feels is self-evident and does not need to be proved.

Premise: a statement that directly supports the conclusion of a syllogism (e.g., 'All lengthy exposure to the sun leads to sunburn.')

Fallacy: a premise that is clearly faulty (e.g., 'All exposure to the sun leads to sunburn').

Proposition: the claim that will be considered in the argument (this can either be true or false, and has to be supported by evidence in order to be proved).

Additional resources are available at:

Mission Critical.
Retrieved from the World Wide Web on 23 October, 2006.
http://www2.sjsu.edu/depts/itl/graphics/main.html

Essays and Arguments: A Handbook on Writing Argumentative and Interpretive Essays.
Retrieved from the World Wide Web on 23 October, 2006
http://www.mala.bc.ca/~johnstoi/arguments/argument1.htm#one

 

Basic principles of inductive reasoning

Inductive reasoning can be 'dangerous' because it relies on generalisations and lends itself to misinterpretation of evidence, e.g., a sample of three or four people's experience of getting sunburnt after four hours in the sun does not necessarily mean that all exposure to the sun leads to sunburn for everyone.

Inductive reasoning is fundamental in science, in which specific observations lead to generalisations after testing the evidence. Inductive reasoning is prone to 'fallacies,' such as the 'floating comparison,' the 'loaded question,' and ' post hoc, ergo propter hoc ' (or false attribution of cause/effect relationships).

Basic principles of deductive reasoning

Deductive reasoning relies on syllogisms, made up of a major and a minor premise and a conclusion. For the conclusion to be valid, the premises have to be true and properly constructed.

The greatest danger in deductive reasoning is not distributing the middle term properly (i.e., the term that appears in both premises). This gives an appearance of sound reasoning, but the conclusion is faulty.

Basic principles of written arguments

A proposition is put forward and supporting evidence provided, and logic is used to develop the proposition and evidence into a case. The introduction raises the topic or subject matter, advances the proposition, defines key terms, makes the thesis statement and indicates the main supporting points. The body of the essay presents and explains the supporting evidence, makes clear transitions between various points, and responds to opposing viewpoints. The conclusion reflects on what has gone before and explains why [and how] the thesis statement has been supported and proved.

Adapted from: Davis, L., & McKay, S. (1996). Structures and Strategies: An Introduction to Academic Writing. South Melbourne: Macmillan, pp. 91-104.

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