Logic and writing
Traditionally, logic has belonged not to English studies, but to philosophy, but the tie between writing and logic is a crucial one. The core of argument (and argument is to be found virtually everywhere) is in logic. Unless one supports a claim or conclusion about something through a logical, or rational, appeal, one is not making a genuine argument. For example, the claim that "Pit bulls should be illegal" is not in itself an argument. By adding to the claim some evidence, "Pit bulls should be illegal because they are dangerous animals," one makes what could be called an argumentative claim. The evidence that pit bulls are dangerous animals supports--makes some headway toward proving--the claim that pit bulls should be illegal. Of course, the evidential part of this claim ("they are dangerous animals") requires a good bit of explanation in an extended piece of writing. The writer might, for example, cite specific instances in which people have been attacked by pit bulls, provide a narrative testimony of a personal encounter with a dog, include scientific data on the strength of a pit bull's jaws vs. those of other domesticated dogs, and so on. In the academic world, we are constantly called on to support and thus examine the worth of claims that we may have unquestioningly presumed to be true. In fact, the ability to understand and practice this operation is a large part of what constitutes a well-educated person.
This site is certainly not the place to go into a lot of detail about formal logic, which can be complicated. What follows is a brief rundown. (Click here for a brief discussion of some of the fallacies commonly used in argument.) There are two general ways of reasoning, of generating a logical appeal: induction and deduction. Brittanica Online defines induction as the "method of reasoning from a part to a whole, from particulars to generals, or from the individual to the universal." Deduction, the inverse to induction, is the method of reasoning from generals to particulars and is the most common form of reasoning in argument. To return to the earlier example, the claim that "pit bulls should be illegal because they are dangerous animals" is a deductive one, because the specific, "pit bulls," is linked to a larger class of things, "dangerous animals"--a class of things that is, in this case, negative and to be avoided. The pit bulls claim, which could function as a thesis sentence in an argumentative paper, is an enthymeme, which is the chief way that logical arguments are built. Most of the time an enthymeme is identifiable by words such as because, since, for, therefore, so, thus, and hence, which signal either the conclusion or the support for an argument. One of the ways to test the validity of such a claim, or enthymeme, is to break it down into what is known as a syllogism, which proceeds from major premise to minor premise to claim:
Note how this syllogism progresses from general to specific, from dangerous animals to pit bulls. Note, too, that our enthymeme (Pit bulls should be illegal because they are dangerous animals) leaves out the general, major premise. This enthymeme, then, like all enthymemes, works by implying a linkage with an unstated idea. Enthymemes work almost in the same way that syllogisms do; an enthymeme is a syllogism which is usually cast in a more conversational form and which is missing either the major or minor premise. By isolating the major premise on which the claim is built, the reader may gain a more critical view of the claim's firmness: What does the claim mean by "dangerous"? Can't Rottweilers and ferrets sometimes be considered dangerous? Wolves and grizzly bears can be dangerous, but they are not, strictly speaking, "illegal." The writer who wants to argue that pit bulls should be outlawed may be required to do more work in building and justifying his basic claim.
There is, of course, much more to be said about the role of logic in writing, especially in argumentation. Any good composition textbook should be able to tell students what they need to know about logic both as a tool of persuasion and as a way of critiquing texts. We conclude this page by looking at one example of an effective use of a logical appeal. Martin Luther King, Jr.'s "Letter from Birmingham Jail," written in 1963, is a direct response to a published statement by eight Alabama clergymen criticizing the civil rights leader for his participation in a nonviolent protest of Birmingham's segregationist policies. This eloquent letter makes a full use of not only logical appeals, but also emotional and ethical appeals (pathos and ethos). His fellow clergymen attack King and the other protesters as lawbreakers; King acknowledges the legitimacy of this concern, and he clarifies the issue by explaining that there are just and unjust laws.
Now, what is the difference between the two? How does one determine whether a law is just or unjust? 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 law that is not rooted in eternal law and natural law. Any law that uplifts human personality is just. Any law that degrades human personality is unjust. All segregation statutes are unjust because segregation distorts the soul and damages the personality. It gives the segregator a false sense of superiority and the segregated a false sense of inferiority. Segregation, to use the terminology of the Jewish philosopher Martin Buber, substitutes an "I-it" relationship for an "I-thou" relationship and ends up relegating persons to the status of things. Hence segregation is not only politically, economically and sociologically unsound, it is morally wrong and sinful. Paul Tillich has said that sin is separation. Is not segregation an existential expression of man's tragic separation, his awful estrangement, his terrible sinfulness? Thus it is that I can urge men to obey the 1954 decision of the Supreme Court [which outlaws segregation in the public schools], for it is morally right; and I can urge them to disobey segregation ordinances, for they are morally wrong.
We note, in conclusion, that this passage works largely through a number of enthymemes which function as argumentative claims. The final independent clause, "I can urge them to disobey segregation ordinances, for they are morally wrong," may be broken down into the following syllogism:
The opening, major, premise is strong, moral, and idealistic (and potentially dangerous when misinterpreted as a license to commit violence). Those who agree with it and act on it should, like King, be prepared to bear its (perhaps unjust) consequences and, when needed, be able to provide a justification for their actions.