A good introductory logic course will discuss the importance of defining terms in any argument. One clear demonstration of using definition in argument is Martin Luther King Jr.’s “Letter from Birmingham Jail,” a letter which King directed at Christian pastors in Alabama in 1963 defending his campaign of nonviolent direct action.

One of the purposes of defining terms is to reduce vagueness. A term is vague when the extent of the meaning is unclear. In the opening of his letter King clarifies the definition of the vague term “outsider”:

I think I should indicate why I am here in Birmingham, since you have been influenced by the view which argues against “outsiders coming in.”

While his opponents apparently defined “outsider” as a person who is not a member of a local community, King redefines it in context as a person who has no interest in the good of the community. He argues that he is not an outsider for three reasons: he was invited to the community; he has organizational ties to the community; and he is compelled as an American to help the community because he perceives their need. He then says,

Injustice anywhere is a threat to justice everywhere. We are caught in an inescapable network of mutuality, tied in a single garment of destiny. Whatever affects one directly, affects all indirectly. Never again can we afford to live with the narrow, provincial “outside agitator” idea.

“Injustice anywhere is a threat to justice everywhere.” Our national leaders would do well to meditate on this.