The unity of a paragraph is determined by and governed by its topic sentence, which is almost always the first sentence in it. The topic sentence not only names the subject of the paragraph, but also makes an assertion about that subject. In a piece of argumentative writing, the topic sentence thus sets out the main line of argument the writer will pursue. It almost always also sets out the specific sub-lines of argument that will be developed in the paragraph in order to support the main line. In other words, it commits the writer to a position that must be proven in the rest of the paragraph. Here's a model from a history text:

Paradoxically an age that described itself in such tones of optimism and confidence also subjected itself to internal criticism of extraordinary severity. Literacy spread, but intellectuals denounced the mass culture it fostered. The arts flourished, but they expressed conflicting values and attitudes that made modern civilization seem lacking in coherence. The standard of living rose, but workingmen formed militant organizations to combat their employers, and socialists considered the very success of capitalism to be evidence of its imminent collapse. Conservatives assailed the threat to civilized values posed by excessive faith in reason, rampant avarice, and purposeless tolerance of every idea and faction. Christians continued to decry materialism and the exclusion of religion from its rightful role. The late nineteenth century is often described as the triumph of the middle class and the age of liberalism, but it was characteristic of that triumph and that age that many were moved to reject it.


Exercise: In each of the following paragraphs, taken from "Morals, Religion, and Higher Education" by Robert M. Hutchins, underline the topic sentence. Because Hutchins is doing unusual, but justifiable, things with his topic sentences, don't go on automatic pilot here. You'll see that working with these unusually structured paragraphs is useful, because you'll learn to attend closely to the thought process in each and because you'll see some future possibilities for your own writing. Be prepared to defend your choice of topic sentence. (I found Hutchins' essay in Edward P.J. Corbett's Classical Rhetoric for the Modern Student, 2nd ed. [Oxford, 1971], 362-378. Hutchins delivered an earlier version of the essay in a speech at Kenyon College in 1948.)

Paragraph 2
By the commitments to which I have referred, higher education may directly contribute to the formation of character. The indirect contributions it may make are, perhaps, almost as important. These are the moral by-products of its intellectual work. The life of learning requires the support of the moral virtues; and an arduous academic career must tend to develop those virtues. Without courage or fortitude no one can long stick at the painful task of thinking and studying. Without temperance no one can resist the momentary pleasures and distractions that interfere with study. Without at least some rudimentary sort of prudence no one can allocate his time and plan his work so as to make the most of his academic opportunities. Without justice, which involves a right relation to one's teachers and fellow-students, no one can conduct himself in the academic community in a way that respects the rights of the mind.

Paragraph 3
If the bulk of the instruction is given by lectures, if the duty of the student is to take notes on lectures and to read textbooks, memorizing material to be regurgitated on the examinations given by the teacher who has taught the course, he may develop the habit of memory and the habit of studying the prejudices or curves of those whose favor he hopes to win. The first of these is a good and important habit, though perhaps not the best or most important of the intellectual virtues. The second is a habit valuable to salesmen, advertising men, college presidents, and others who spend their lives trying to get something from other people. But it is a habit into which most Americans seem to fall naturally; they do not need to go to college to get it. The value of the discussion method of instruction, of demanding a great deal of independent work from the student, and of a system of external examinations that requires study of the subject rather than the teacher, is that the habits of action, as well as the habits of thought and knowledge, formed by these means are closely analogous to, if they are not identical with, the four cardinal virtues.

Paragraph 4
An educational institution should be a community. A community must have a common aim, and the common aim of the educational community is the truth. It is not necessary that the members of the educational community agree with one another. It is necessary that they communicate with one another, for the basis of community is communication. In order to communicate with one another, the members of the community must understand one another, and this means that they must have a common language and a common stock of ideas. Any system of education that is based on the training of individual differences is fraudulent in this sense. The primary object of education should be to bring out our common humanity. For though men are different, they are also the same, and their common humanity, rather than their individual differences, requires development today as at no earlier era in history.