Having a balance between the three is essential for total honesty with the self, but most public speakers draw too heavily on the Pathos and ignore the Logos altogether. I have found that the most effective arguments are those that come entirely from a logical perspective; on the other hand, if you have no personal involvement with the issue at hand, it can be hard to care, so Pathos is very useful when appealing directly to an emotional issue. I prefer Logos in my rational thought, but I understand and accept my Pathos response when it comes to issues that are important to me.
When I teach this to my students I usually reference singer Sarah Mclachlan's public service announcement in support of abused animals. The commercial is dripping in pathos as pictures of sad looking animals flash across the scene while her plaintive song, "Angel," plays in the background. Her ethos is established when she talks about her own love of animals and her past associations with the ASCPA, and her logos is established when she talks about the statistics about the number of animals in need of homes and how relatively affordable it is for us, the audience, to support these shelters and help take care of these sad animals.
They are all different ways to persuade. Sometimes which one you use depends on the audience, and sometimes it depends on your purpose. For example, if you were presenting or writing to doctors, you might use logos. However, for a tv commercial aimed at teens you would probably use ethos.
When I teach my students about Persuasive or Argumentative essays, I usually teach these three devices along with it. We mostly focus on the basic 5-paragraph essay and the students sometimes wonder where to put each device. After analyzing my own writing, I usually opened with Ethos in the introduction; then, I used mostly Logos throughout the body paragraphs; and finally, I drive home the conclusion with Ethos and Pathos. This way, I don't focus on the pathos too much and use my evidence and quotes within the body paragraphs with the Logos. But of course, style is up to the writer. Beginning writers seem to like the writing map because they never know what to say when. These devices can be arranged in a person's own style when outlining an essay.
Much depends on knowing your audience. Some audiences will be more receptive to ethos and/or logos than pathos. If you are delivering a paper that is based on a scholarly argument, you should focus on these rhetorical forms. However, if you are addressing a political topic, for instance, using pathos sometimes helps to put a human face on an issue. That's why politicians always reference people with compelling stories (people who have lost their houses, or can't get an operation due to lack of insurance, etc) in their speeches.
From the Greek, "logos" originally meant "word," "speech," "account," or "reason," but over time has taken on a new meaning. Related to philosophy, psychology, etc., it can refer to a plan or an account. The dictionary definition is "the rational principle that governs and develops the universe." (Logo- comes from the Greek, meaning "reason.")
Pathos deals with the expression of the emotional. (In Greek páthos means "to suffer.") It appeals to the emotions of a group when included in a play, for instance.
Ethos deals more with society: the beliefs or customs of a culture. (From the Greek, it means "custom, habit, character"). It deals with one's "guiding beliefs."
So Logos deals with reasoning; pathos deals with emotions; and, ethos deals with the common practices of culture or a group.
A strong argument will have neither too much nor too little of each of these concepts. Too much emotion, or pathos, and the speaker risks offending those who don't agree, coming across too strongly, or otherwise putting people off. Not enough emotion, and the reader will not be drawn into the argument. Ethos is another tricky concept in practice. The speaker will want to seem knowledgeable but not arrogant. They will want to show they have experience and expertise in this area without seeming dogmatic. Logos is probably the easiest of the three concepts. Here the speaker simply supplies facts and logic to support their case and cause. These three types of arguments are often wound together. For instance, it is possible to show an emotional connection while offering up factual evidence.
The three terms of Greek origin refer to rhetorical methods of trying to persuade your audience to agree with your view point. We associate them with the study of persuasive speeches or documents that seek to sell an idea or concept. Pathos is an appeal to the emotions, ethos is a device based on who the speaker is and their expertise, and logos is an appeal that is made based on facts. The strongest arguments are those that combine all three approaches.
Pathos is an appeal to emotion. It's when you say "we should increase spending on health care because it's sad when babies die from lack of care."
Ethos is an appeal to the audience based on who the speaker is. It is when you say, "Based on my years of research in the health care field, I say that we should..."
Logos is an appeal based on logic and facts. It is when you say "We should increase spending on health care because we will save more (from people being healthier and more productive) than we spend.
All of these can be used in essays or in speeches to persuade the audience to agree with the speaker.