Reasoned argument is called for when informed people disagree over an issue or remain divided over how best to solve a problem, as is so often the case in social and political life. Hence, the thesis statements in reasoned arguments make arguable assertions—possibilities or probabilities, not certainties.
Therefore, a statement of fact could not be an arguable thesis statement because facts are easy to verify—whether by checking an authoritative reference book, asking an authority, or observing the fact with your own eyes. For example, these statements assert facts:
Jem has a Ph.D. in history.
I am less than five feet tall.
Eucalyptus trees were originally imported into California from Australia.
Each of these assertions can be easily verified. To find out Jem’s academic degree, you can ask him, among other things. To determine a person’s height, you can use a tape measure. To discover where California got its eucalyptus trees, you can search the library or Internet. There is no point in arguing such statements (though you might question the authority of a particular source or the accuracy of someone’s measurement). If a writer asserts something as fact and attempts to support the assertion with authorities or statistics, the resulting essay is not an argument but a report.
Like facts, expressions of personal feelings are not arguable assertions. Whereas facts are unarguable because they can be definitively proved true or false, feelings are unarguable because they are purely subjective.
You can declare, for example, that you detest eight o’clock classes, but you cannot offer an argument to support this assertion. All you can do is explain why you feel as you do. If, however, you were to restate the assertion as “Eight o’clock classes are counterproductive,” you could then construct an argument that does not depend solely on your subjective feelings, memories, or preferences. Your argument could be based on reasons and support that apply to others as well as to yourself. For example, you might argue that students’ ability to learn is at an especially low ebb immediately after breakfast and provide scientific support for this assertion—in addition, perhaps, to personal experience and reports of interviews with your friends.