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Similarity / Difference
That topic of invention which invites us to consider how something compares and contrasts with others. One use of this topic is arguing by analogy, using the logic that if two things are similar in one or two ways, they are likely similar in another characteristic. Another use of this topic is drawing a conclusion based on an example of one instance of similarity.

In your statement you assert that our actions, even though peaceful, must be condemned because they precipitate violence. But is this a logical assertion? Isn't this like condemning a robbed man because his possession of money precipitated the evil act of robbery? Isn't this like condemning Socrates because his unswerving commitment to truth and his philosophical inquiries precipitated the act by the misguided populace in which they made him drink hemlock? Isn't this like condemning Jesus because his unique God-consciousness and never-ceasing devotion to God's will precipitated the evil act of crucifixion? We must come to see that, as the federal courts have consistently affirmed, it is wrong to urge an individual to cease his efforts to gain his basic constitutional rights because the quest may precipitate violence. Society must protect the robbed and punish the robber.
—Martin Luther King, Letter from Birmingham Jail

The following use of the topic of similarity/difference is an argument by analogy:

Administrative work is like juggling a chain saw: once in a while you pull it off and really wow people...

Related Figures
See Also
  Sources: Cic. Top. 3.15-16, 10.41-11.46 ; Suarez 13r-v

A topic of invention that invites one to look at issues of "more" and "less."

Aristotle proposed considering these criteria to generate ideas using the topic of degree. Each of these can be inverted:

  1. A greater number of things is often considered better than a small number of the same things
    Example : We need less war and more peace.
  2. That which is an end is a greater good than that which is only a means
    Example : Exercise is all good and well, but should be avoided if it actually threatens one's health.
  3. What is scarce is greater than what is abundant.
    Example : This was no common pebble to be found on any road or byway; it was a blue diamond, more rare than any other of its kind.
  4. What learned people would choose is better than what the ignorant would choose.
    Example : All of your friends may be handling their uranium collection without lead gloves, but your uncle the nuclear physicist has told you the best course.
  5. What the majority of people would choose is better than what the minority would choose.
    Example : You're watching the network watched by more Amercans than any other...
  6. What people would really like to possess is a greater good than what they would merely like to give the impression of possessing.
    Example : Health is a greater good than justice, because while people can be content with the mere reputation for being just, they prefer being healthy to only seeming healthy.
  7. If a thing does not exist where it is more likely to exist, it will not exist where it is less likely to exist
    Example : In his famous poem "Death, be not proud," John Donne compares death to sleep. To paraphrase the argument that he makes, we all derive a great deal of pleasure from rest and sleep; therefore, we should derive even more pleasure from that which rest and sleep imitate: death. If there is so much pleasure from the lesser thing, there is to be so much more pleasure from the greater thing. This is often referred to as arguing a fortiori (Latin: "from the stronger")
  Sources: Cic. Top. 18.68-71

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Gideon O. Burton, Brigham Young University
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