When we argue from analogy, we say that something is like something else. For instance, we could argue that having two women's professional basketball programs — the American Basketball Association (ABA) and the Women's National Basketball Association (WNBA) — is a big mistake for the future of the sport. We can say this is like the experience of the two men's leagues in professional football in that back in the early 60s the National Football League (NFL) and the American Football League (AFL) were killing each other off in terms of divided fan support and media attention until they decided to merge and combine the merits of both leagues into one super league.
The writer must be fair in claiming likeness, however. Has the time passed since the merger of the two football leagues changed the climate of the country, the way that people watch sports? Is there something different about men's and women's sports that would make two leagues in a women's sports feasible where it wasn't in a men's sports? Would the enormous difference in the price of tickets make a difference?
Another example: Is it fair to say that those who resist the argument that we must do something at once about the depletion of the ozone layer are like those who refused to see the "truth" about smoking or those who refused to accept scientific evidence about evolution? You can argue it, but it is still only an analogy and may not prove anything at all. Be careful in your use of analogies in your argument paper. It may prove helpful, but it may be misleading. An inappropriate analogy is a fallacy known as the false analogy.
The other sub-sections of this part of Principles of Composition are as follows: