Arguments come in two forms: deductive and inductive. A
deductive argument is intended to provide logically conclusive support for
a conclusion; an inductive one, probable support for a conclusion.
Deductive arguments can be valid or invalid; inductive arguments, strong
or weak. A valid argument with true premises is said to be sound. A strong
argument with true premises is said to be cogent.
Evaluating an argument is the most important skill of critical
thinking. It involves finding the conclusion and premises, checking to see
if the argument is deductive or inductive, determining its validity or
strength, and discovering if the premises are true or false.
Finding Missing Parts
Sometimes you also have to ferret out implicit, or unstated,
premises. Finding implicit premises is a three-step process.
Arguments can come in certain common patterns, or forms. Two
valid forms that you will often run into are modus ponens
(affirming the antecedent) and modus tollens (denying the
consequent). Two common invalid forms are denying the antecedent and
affirming the consequent.
Using the counterexample method can help you determine whether
a deductive argument is valid or invalid.
Analyzing the structure of arguments is easier if you diagram
them. Argument diagrams can help you visualize the function of premises
and conclusions and the relationships among complex arguments with several
Assessing very long arguments can be challenging because they
may contain lots of verbiage but few or no arguments, and many premises
can be implicit. Evaluating long arguments, though, requires the same
basic steps as assessing short ones: (1) Ensure that you understand the
argument, (2) locate the conclusion, (3) find the premises, and (4)
diagram it to clarify logical relationships.