An argument's grounds answers the questions, "How do you know that?" and "Why?", which people ask when they confront a claim. "Grounds" is just another word for reason. The reason for a claim goes by many different terms: support, evidence, data, reason and premise. All of them refer to the statement brought forward to establish the "truth" of a claim.

Grounds are often
though by no means alwaysidentifiable by the fact they immediately follow the word "because."

Grounds fall into one of three major categories, though there are subcategories.

Aristotle, the first and perhaps still most cited theorist of rhetoric, writes in his Rhetoric about the three "modes of persuasion" that may be found in a speech. These are known by two other terms: "artistic proofs," meaning they are means of persuasion (proofs) that come from the craft (art) of the speech, as opposed to another source (e.g., testimony obtained under torture); and the "rhetorical appeals." They all form the basis or grounds on which a claim is made. You may know them as ethos, pathos and logos.

Ethos (Appeal to the Speaker)

The first of these modes of persuasion is ethos, or appeal to the credibility of the speaker, which Aristotle believed the most important. Aristotle observes that, when it comes to believing people, we're more apt to believe the person we believe to be of good character than the one we believe is a scoundrel, especially "when exact certainty is impossible and opinions are divided." In other words, when there are no clear answers in a controversy, people lend the most credent ear to those they think are well disposed to them.

Some people talk about ethos as though it is the credibility of the speaker that comes from his or her preceding reputation. Not according to Aristotle. According to him, a speaker's reputation and ethos are separate and distinct: ethos is that part of the speech itself which seeks to communicate something about the character and so credibility of the speaker.

Simply put, ethos is anything in the speech or writing in which the speaker is trying to communicate, "Trust me. I'm on your side, and I know what I'm talking about."

When writing for academic audiences, writers often borrow ethos from others by citing authorities. By calling upon a noted authority in the field, one is, in effect, attempting to bring that source's credibility from elsewhere to one's own writing. As Nancey C. Murphy writes, ethos, though not often overtly stated, is very important to academic forms of writing.

NB: Ever since Aristotle, we have talked about ethos and pathos as though they were completely separable. However, because a speaker's perceived character will ultimately be judged based upon common beliefs shared by the audience, any appeal to ethos is necessarily and fundamentally an appeal to pathos, or audience interest. We may, though, talk usefully about ethos as a separate kind of appeal, one in which attention to the speaker (or to one's sources) is particularly highlighted.

Pathos (Appeal to the Audience)

The second of the modes of persuasion is pathos, or appeal to the audience's emotions, passions and interests. Any appeal to an audience's sense of self-preservation, morality, religious or patriotic duty, pity, hatred and so on would all be examples. The whole point of pathos, as Aristotle all but says, is to bias the audience's judgment: "Our judgments when we are pleased and friendly are not the same as when we are pained hostile."

Academic audiences, if asked, will say they tend not to accept pathos when they are hearing a lecture or reading a paper. And yet, as Murphy points out, there are ways of sneaking pathos in by means of loaded language meant to excite certain emotional reactions. Much advertising trades on pathos.

Logos (Appeal to the Message)

The third of the modes of persuasion is logos, or the use of logical reasoning. This has to do with the rational relationship between propositions, and they have nothing to do with whether the audience believes the rhetor to be credible or how the audience interprets the content as bearing on its interests. Logos refers to what is often called the "demonstration," that is, showing the truth or validity of a claim by means of proofs.

Academic writing puts a premium on logos, as academicians are interested in new understanding based on previously established knowledge. Showing the logical relationship between old and new information is one of the most important skills required by academic discourse.

The Rhetorical Triangle

Commonly, ethos, pathos and logos are graphed together in the famous "rhetorical triangle." The purpose is to show the relationship between the speaker, the audience and the message. Here is one example of this triangle.