" Thesis . This advanced exercise [one of the progymnasmata ] asks the student to write an answer to a 'general question' ( quaestio infina )--that is, a question not involving individuals. . Quintilian . . notes that a general question can be made into a persuasive subject if names are added (). That is, a Thesis would would pose a general question such as 'Should a man marry?' or 'Should one fortify a city?' (A Special Question on the other hand would be 'Should Marcus marry Livia?' or 'Should Athens spend money to build a defensive wall?')"
(James J. Murphy, A Short History of Writing Instruction: From Ancient Greece to Modern America , 2nd ed. Lawrence Erlbaum, 2001)
In writing an essay , a thesis statement determines the worth of an essay by its capacity to stay focused on its thesis statement. For an instance, if a writer fails to clearly mention or define a solid thesis statement in his or her essay, it will be almost impossible for him or her to pay attention to the issue he or she plans to discuss and explain. Suppose a writer wants to write an essay on how to make a perfect fruit salad, the quality of his or her writing will exceedingly improve if he or she lets the readers have knowledge of the subject matter at the start of the essay: