The easiest way to explain what rhetoric means is with one simple sentence: it is persuasion. A more complicated definition, is that rhetoric is one person trying to change another person's opinion, whether orally or in a written work, and by using effective language. Nowadays, it may have negative connotations for seeming like it lacks facts or substance, but rhetoric is actually achieved by specifically analyzing how one phrases things, and by appealing to the audience, and as well as different aspects of humanity, such as emotion or logic.
First, on the top of the triangle is Ethos, as Aristotle originally called it when he originally named and explained what rhetoric was, or the speaker, as it is now called. This area deals with credibility. For one' argument to be able to convince others, the speaker themselves must appear like they know what they are talking about. If the speaker doesn't seem believable or knowledgeable in the subject, than their argument loses all of its credibility, and the rhetoric will be weak. In "Freakonomics," the authors obtain their credibility or logos by discussing their experience with economics. Most of the book however, is composed of accounts and studies of others, and their credibility is obtained by discussing their education and credentials, such as being students of Economics, or even professors, as well as at one point a Criminologist.
Next is Pathos, or the Audience. This aspect deals with emotion. To convince others of an argument, one must appeal to their emotions, and convince them of the issues or values that are at sake. These emotional appeals must also be tuned specifically towards the audience the speaker is trying to reach. If the author appeals to values for a different demographic than the target audience, than the argument isn't going to succeed. In "Freakonomics," pathos is rarely used. The author depend only on logic, facts, and data to explain their points. In fact, throughout the book, they even show how pathos and emotions made false arguments seem believable, despite the overwhelming facts, such as when pointing out how crime rates went down. While many of the arguements listed relied on people's emotions, such as better and more police, as well as the economy, the facts provided showed that there was a correlation between the legalization of abortion and the sinking of crime rates. The book then points out how no one wants to achknowlage this, because of their emotions clouding their judgement.
What "Freakonomics" relied on was the last aspect of the rhetorical triangle, Logos, or the message. For this part of an argument, one's points must make sense. There must also be facts, data, or other forms of information that support it. If the rhetoric is not logical, it will not be believable. Just like in the book, how facts prove their arguments right, and the others wrong, such as with the abortion and crime rates, or with baby names linked to income and future success.