One practical method of organizing arguments is to identify relationships between terms. Terms may be related as different parts of a whole (including different steps in a process) or as different species of a genus. In his “Letter from Birmingham Jail” Martin Luther King Jr. uses both methods of relating terms to organize and clarify his arguments.
Dr. King first distinguishes parts of a whole as he identifies the steps in the process of his campaign of nonviolent direct action:
In any nonviolent campaign there are four basic steps: collection of the facts to determine whether injustices exist; negotiation; self-purification; and direct action.
He explains how he has followed these steps in Birmingham, and how each step led to the next. This use of arranging the parts of a process lends clarity to his argument.
Near the end of the letter he uses the concepts of species of a genus as he distinguishes two species of law: just and unjust:
One may well ask: “How can you advocate breaking some laws and obeying others?” The answer lies in the fact that there are two types of laws: just and unjust. I would be the first to advocate obeying just laws. One has not only a legal but a moral responsibility to obey just laws. Conversely, one has a moral responsibility to disobey unjust laws. I would agree with St. Augustine that “an unjust law is no law at all.”
He then defines each of these species of law in order to clearly distinguish them:
A just law is a man-made code that squares with the moral law or the law of God. An unjust law is a code that is out of harmony with the moral law. To put it in the terms of St. Thomas Aquinas: An unjust law is a human law that is not rooted in eternal law and natural law.
This demonstrates the value of distinguishing and defining terms in argument.