CONSTRUCTING A LOGICAL ARGUMENT

What is an argument?

An argument is an effort to justify a particular conclusion. The justification should be strong enough to persuade others that your conclusion is the correct one.

What is an argument composed of?

Every argument consists of premises and a conclusion. The premises are particular statements that provide the reasons or evidence supporting your conclusion. The conclusion is, of course, the position that you are arguing for.

 Types of Argument:

Type: Deduction

Definition: This form of argument is based on the rules of logic, so if the premises are true, then the conclusion must also be true.

Example: If you smoke, you might get lung cancer. You smoke. Therefore, you might get lung cancer.   

What makes it strong? : Deduction is always strong because it is based on logical connections between premises and conclusion. It is important, however, to establish the truth of the premises.

Type: Induction

Definition: This form of argument involves reasoning from particular facts or observations to draw conclusions about general principles.

Example: Ann smoked and she has lung cancer. Emile smoked and he has lung cancer. In fact, every smoker I know now has lung cancer. Therefore, if you smoke you will have a good chance of getting lung cancer.

What makes it strong? : The strength of inductive arguments depends on the number of observations supporting the generalization.  The more observations there are, the more likely the conclusion is true. Note that every counterexample reduces the likelihood that the conclusion is true.

Type: Abduction

Definition: The conclusion is considered to be the best explanation of the available facts. 

Example: Several studies establish a high correlation between smoking and lung cancer. Additional studies demonstrate that incidence of lung cancer in ex-smokers and non-smokers is much lower. Therefore, it is likely that smoking causes lung cancer.

What makes it strong? : The strength of abductive arguments depends on the degree to which the conclusion accounts for all evidence and data, including that which appears to be contradictory.

Type: Analogy

Definition: The conclusion is derived from comparing the issue at hand with another, similar issue. 

Example: Breathing in a toxic substance like asbestos is known to cause lung cancer. Cigarette smoke is also toxic, so it likely causes lung cancer.

What makes it strong? : Arguments from analogy are only strong when the two issues are similar with respect to the key features that are significant to the conclusion.