An enthymeme is a syllogism with one or two parts of its argument—usually, the major premise—missing. In everyday life, we often leave out parts of arguments—most of the time because we think they are so obvious (or clearly implied) that they don’t need to be stated. We assume that the people hearing or reading the arguments will easily be able to fill in the missing parts.
Many enthymemes are presented as a conclusion plus a reason. Consider the following enthymeme:
Robert has lied, so he cannot be trusted.
In the statement above, the minor premise and the conclusion are stated, but the major premise is only implied. Once the missing term has been supplied, the logical structure of the enthymeme becomes clear:
It is important to identify enthymemes in arguments you read because some writers, knowing that readers often accept enthymemes uncritically, use them intentionally to unfairly influence readers.
Consider this enthymeme:
Because Liz receives a tuition grant, she should work.
Although some readers might challenge this statement, others will accept it uncritically. When you supply the missing premise, however, the underlying assumptions of the enthymeme become clear—and open to question:
Perhaps some people who receive tuition grants should work, but should everyone? What about those who are ill or who have disabilities? What about those who participate in varsity sports or have unpaid internships? The enthymeme oversimplifies the issue and should not be accepted at face value.
At first glance, the following enthymeme might seem to make sense:
North Korea is ruled by a dictator, so it should be invaded.
However, consider the same enthymeme with the missing term supplied:
Once the missing major premise has been supplied, the flaws in the argument become clear. Should all nations governed by dictators be invaded? Who should do the invading? Who would make this decision? What would be the consequences of such a policy? As this enthymeme illustrates, if the major premise of a deductive argument is questionable, then the rest of the argument will also be flawed.