Rhetoric is the art of or study of using language effectively in writing or speaking. Since an effective writer/speaker will persuade a reader/listener of his/her own viewpoint, rhetoric is even more specifically the "art of persuasion" (Brigham Young University, "What is rhetoric?"). One aspect of persuasion is effectively presenting an argument. There are many different ways to present an argument, and we call these methods rhetorical strategies. There are many different rhetorical strategies, and an effective rhetorician will use more than one strategy in an argument. Two rhetorical strategies are comparison/contrast and "cause and effect analysis" (Northern Virginia Community College, "Rhetorical Strategies for Essay Writing").
When we use comparison/contrast to present in an argument, we look at and present the similarities and differences between two subjects. To compare is to present the similarities; to contrast is to present the differences. But, more specifically, we compare and contrast to prove an overall point about the two subjects, to show an overall connection between the two subjects.
When we conduct and present a "cause and effect analysis," we are either looking at and presenting what caused something or what future effects something will have. For example, if we are analyzing global warming, we might look back at the past to see all that has happened to lead up to global warming. In this case, we would be analyzing the causes of global warming. If we want to analyze the effects of global warming, we would look at what can happen in the future as a result of global warming.