Posted on behalf of Peter:
Critical Thinking provides a set of tools to assess the truth of arguments (argument = ‘attempt to persuade by reason’). Arguments that we need to analyse are everywhere: media commentators, financial advisors, business proposals – in fact anywhere where we need to decide if we should believe someone’s line of reasoning (including our own…).
An argument has one or more premises leading to a conclusion. Premise and conclusion are types of statement. Assessing an argument basically involves asking the following two questions. (1) Can I rely on the information used in the premises i.e. is it true, false, biased, complete etc. (2) Can I rely on the way the argument structure is used ?
There are two major types of argument: Deductive and Inductive. There is also a third type, Abductive, that tends to be used mostly in relation to scientific enquiry. Each major type has a set of associated thinking errors, or ‘fallacies’.
Deductive arguments deal in certainty. A ‘valid’ deductive argument is one where, if the premises are true, the conclusion must also be true. If the premises are in fact true then the argument is also ‘sound’. A deductive argument can be ‘invalid’ (even if the premises are true, the conclusion could be false) or ‘unsound’ (the premises are objectively false). An example of a valid, but unsound, argument would be: ‘All Greeks are green. Socrates was a Greek. Therefore Socrates was green’.
Inductive arguments are those seen most often in daily life, and are based more on probability / rational expectation than certainty. The equivalent of deductive validity is ‘inductive force’ (probability of conclusion being true greater than 0.5). The equivalent of deductive soundness is ‘inductive soundness’. An argument is inductively sound if its premise(s) are true and the structure is inductively forceful e.g.: ‘John rarely hands his homework in on time. Therefore it is likely to be late again tomorrow’.
Much scientific development is based on inductive reasoning i.e. if an experiment is testable and repeatable, then a general rule may be able to be built. However abductive reasoning is also used. Here, faced with an event or set of circumstances, a number of possible hypotheses are developed to explain the event. The most plausible explanation is then taken as a provisional explanation (subject to further testing).