The first of Campbell's four types of moral reasoning is "experience." As the title suggests, "experience" is based on our own perception and observation. Campbell felt that through trial and error, our own experience in rhetoric will strengthen our sound and justified arguments. In contrast, experience will weed out the weak or unsound arguments we make, improving our overall rhetorical abilities.
The second type of Campbell's theory of moral reasoning is "analogy." Campbell contrasted rhetorical analogy with experience, claiming that "analogy" is based off of our indirect experiences, such as hypothetical thought. Campbell suggested that numerous analogies be used in rhetoric because a single analogy can be defeated much easier by an opponent. Campbell suggested the rhetorical use of analogies primarily as an argumentative defense rather than a means to strengthen our own arguments.
The third of Campbell's four types of moral reasoning is "testimony." This is a type of rhetorical reasoning based off of the experiences of others. Just as with our own experiences, we can turn to the experiences of others in order to strengthen our own arguments. Except for cases where a generalized conclusion is reached through an experimental study, Campbell felt that the testimony of others is a stronger rhetorical tool than our own experience.
The final type of Campbell's theory of moral reasoning is labeled as the "calculation of chances." When the other three types of moral reasoning are insufficient for an argument, the arguer can turn to mathematics in order to strengthen an argument. Because mathematics are objective, Campbell's "calculation of chances" works as a fail-safe in rhetorical debate. By mathematically analyzing past experiences in the context of the present argument, the arguer can create a statistical probability in support of the argument being made.