Welcome to logical reasoning in speeches. Public speakers beware! Errors in reasoning
are also known as logical fallacies. The eight most common logical fallacies are: ad hominem
ad absurdum (including the straw man argument), either or fallacy,
post hoc ergo propter hoc, ad varicundium, ad populum, red herring, and slippery slope.
Ad hominem. Speakers who use this technique attack the integrity of a person to weaken
that person's argument. For example: rather than deal with the substance of the real issue
(such as environmental concerns for example), the speaker says "how can you trust this bureaucrat!"
Ad absurdum. Speakers who use this technique extend the argument to ridiculous extremes.
For example: a teenager says to her parents when they disallow her going out one night "well fine,
you might as well send me to the convent!"
A variation of ad absurdum is the straw man argument.
The name straw man implies a flimsy argument that is knocked down. The straw man argument is a weak
example that a speaker uses to suggest that it represents the entire population. For example:
"Some of our students don't own a computer. We shouldn't have students use computers in school!"
Either or fallacy. Speakers attempt to force a choice between two alternatives as if those are
the only two. For example: "Either we build a new school or our children will never go to college!"
Post hoc ergo propter hoc. Better known as false cause. For example: if a black cat crosses your
path and five minutes later you fall and break your arm, the cat was the cause of your bad luck.
Ad varicundium. Appealing to an authority for your argument the problem is the authority may not be
the authority on that issue. For example: remember years ago when then football player Joe Namath was
endorsing a specific brand of pantyhose? Joe may not have been a real expert on that issue.
Ad populum. Often called jumping on the bandwagon. For example: recall those conversations with your
parents when you asked them if you could do something because all of your friends were.
Their response may have been "if they all jumped off a cliff would you too?"
Red herring. Fish has a strong odor. It is said that farmers in England used to drag
a fish along the edge of the fields to keep hunters and hounds off track. Speakers who
use the red herring technique divert attention from the subject of discussion. For example:
why should we worry about the amount of violence on television when thousands of people are killed
in automobile accidents each year. The number of people killed in automobile accidents is a serious
problem but it has no bearing on the question of whether there is too much violence on television.
This is a red herring (or a stinky fish dragged across the trail to divert the attention from
the real problem). Slippery slope: The fallacy lies within the assumption that point A leads
to point B then to point C and so on. For example: "If you require background checks on
gun purchases the next thing is registration, then outlaw ownership, then confiscation!"
You have just learned about eight common logical fallacies. Logicians have identified in excess
of 125 logical fallacies. This concludes this learning object on logical reasoning in speeches.