The thesis statement of an argument, no matter how long the argument, has the same relation to that argument that a topic sentence has to its paragraph. In other words, just as a paragraph has a kind of “syntax,” so does an entire argument. The thesis also governs the argument by committing you to a position that you must prove in the argument that follows.**

Because your thesis commits you to a certain argument, you need to be quite sure about what that commitment entails. Specifically, you need to know what topics must be dealt with and what relation(s) must be proven among those topics. (Inexperienced writers often notice the former and neglect the latter, which is like recognizing that the subject of a topic sentence needs to be dealt with, but not that what’s predicated about the subject also needs to be treated.) For instance, in analyzing the thesis statement Binney and Smith revolutionized the children’s art world with the Crayola line, it is not enough to note that the topics of the argument are a) Binney and Smith’s Crayola line and b) the children’s art world. The thesis proposes a relation between the two, that “a” caused a specific (“revolutionized”) effect in “b,” which the writer must prove.

As you can see, analyzing the syntax of your thesis statement is one way to discover what it obliges you to prove. You especially want to note the grammatical subject and the predicate. In our example sentence, Binney and Smith is the grammatical subject, and revolutionized the children’s art world with the Crayola line the predicate. (This is the moment, by the way, to check that the grammatical subject of your thesis is in fact the topic about which you mean to write. If your assigned topic is, say, Crayolas, then your sentence is not well structured, because the topic of the argument is, grammatically, in the very subordinate position of object of the preposition.) You can further analyze the predicate into verb and direct object. You now have the complete set of relations: the subject (a) is related to the direct object (b) through the verb (c). Therefore, the nouns (a) and (b) are the topics of your argument, and (c) is the relation you must prove. You can also recognize that, subsidiary to your main argument, your prepositional phrase asserts the means by which a and b are related.

Another way to discover at least the relation(s) you must prove is to look for the transitions within your thesis or, if there are none, to temporarily restructure that thesis so that you have one. Our example sentence, which is grammatically just fine, has a simple structure and therefore no transitions, but you could restructure it to make more clear the relations among terms: Because Binney and Smith introduced the Crayola line, the children’s art world was revolutionized. You can see now that the relation you have to prove is one of cause and effect. Whether you use the first or second method, what you are doing is determining the point at issue, to use an expression that rhetoric long ago borrowed from law, the point on which your argument will turn.

This determination of the relation between terms reveals, as you can see, the line or lines of argument you must pursue to prove your thesis. These lines of argument are limited. In brief, they are

  • definition: a is b or a is not b;
  • relationship:
    • cause and effect: a is the cause of b;
  • comparison
    • similarity: a is the same as b;
    • difference: a is not the same as b;
    • degree: a is similar in kind to b, but differs in some degree (more important, more dangerous, less complete, etc.) from b.

See “Discovery of Arguments,” “The Topics,” in Chapter 2 of Edward P.J. Corbett and Robert J. Connor’s Classical Rhetoric for the Modern Student, 4th edition (Oxford, 1999) for a much more developed discussion of lines of argument.

You may find that you have not only a major line of argument, but also some minor or supporting lines of argument. In, for instance, the thesis, The policy of workfare will never be successful, because it assigns jobs which are dull and demoralizing and which, as a result, create unwilling recipients, the major line of argument is obviously cause and effect (it’s also, by the way, an evaluation argument): the independent clause must be shown to be an effect of the dependent adverbial clause structure. But within the dependent adverbial clause, the two dependent adjectival clauses must also be shown to stand in a causal relation to one another. In brief, the topics to be dealt with are policy of workfare, jobs, and recipients.

Exercise: First diagram each of the following thesis statements. Then provide a complete analysis of what must be proven. Indicate both the topics that must be addressed and the line(s) of argument, the relation(s) among those topics.

1. The social, political, and cultural atmosphere of the Impressionist Era had an adverse effect on the reception of the art of the period.

2. The life of Martin Luther King, Jr. serves as a model for all those who strive for civil rights today.

3. The lack of challenge found in many secondary schools can be remedied through different levels of classes and stricter demands on the students.

4. In “Consolations,” Linda Pastan’s metaphors illustrate the passage of time and the inadequacy of written communication.

5. The two sonnets by John Milton are fundamentally different, despite a remarkable similarity between their religious subjects, in the ways they speak of human activity and existence.

*All of the thesis statements used in this section are versions of ones former students wrote.

**Obviously, then, the thesis of an argument must be an arguable statement; it differs from the thesis of a report or an exposition. For instance, Insurance companies argue that owning small animals increases the expected life span of senior citizens is the thesis statement of a report on the findings of the companies, not the thesis statement of an argument. As given, this statement is not arguable. One way to establish whether or not you have an arguable statement is to ask yourself what the opposing argument is.