A genetic fallacy is an illogical argument for or against an idea based on the origin of the idea. An example of a genetic fallacy is the statement “It will rain on Tuesday because my father said so.” The speaker’s father may be a good man and a good father, but it doesn’t necessarily translate that he knows for certain what the weather will be some time in the future. Another statement that illustrates the genetic fallacy is “This book is horrible—after all, look who wrote it.” Those who commit the genetic fallacy offer evaluations based solely on the source of a thing or the history of an idea, rather than judging the actual merits (or demerits) of that thing or idea.
In John 2, Nathaniel is invited to meet Jesus of Nazareth, and Nathaniel comes close to committing a genetic fallacy: “Nazareth! Can anything good come from there?” he says (verse 46). In other words, Nathaniel considered all Nazarenes to be nobodys—a man’s hometown was enough to form an opinion of the man. But Nathaniel’s reasoning was faulty. Jesus, although He was from Nazareth, was indeed the promised Messiah.
The genetic fallacy sometimes shows up in arguments regarding religion. The reasoning usually follows these lines: “That person’s faith is irrelevant because he most likely learned that faith from his parents.” Notice that such a declaration makes no attempt to evaluate the validity of the faith or its relevance; it simply rejects it based on the idea that exposure to religion as a child negates its truth or somehow lessens its relevance in adulthood.
The genetic fallacy is fallacious because the truth of a statement is in no way based on the origin of the concept. Even a usually less-than-credible source can be right sometimes. And even the most trusted sources can at times get their facts wrong (barring divine inspiration). A philosophical or theological concept is either true or it is not; it does not matter how a person came to believe the concept or who, in the past, held that concept to be true.
At the same time, arguments regarding origins in religion do bear consideration. People should not blindly follow a religion merely because it is the religion of their parents. Each individual is responsible for his or her own beliefs and relationship with God. Although a faith learned in childhood is not necessarily false, it is also not necessarily true. Believers should study the Scriptures (Acts 17:11) and be able to account for why they believe what they do (1 Peter 3:15), apart from family or church tradition.