You should always know how to present what you have to say, even if it'll cause a passionate discussion, in a well respected manner. These are the most common fallacies everyone should know, to avoid using and to identify in others!
Ten Common Fallacies Everyone Should Know
Fallacies: Incorrect or misleading beliefs or opinions based on inaccurate facts or invalid reasoning.
When someone attacks the person instead of the argument.
Example: "Jordan's just a stupid blonde on unemployment. Why would you ever consider her strategy for getting a job." "Mike cheated on his final exam. You can't trust him to know the answers to any of your questions."
Appeal to Authority
When a statement is considered true because it's made by someone who is considered an "authority" on the topic.
Structure: Source A says that "Q" is true. Source A is authoritative. Therefore, "Q" is true. Example: "My doctor says taking St John's Wart everyday will make me less depressed. He should know, he's a doctor!"
"The policeman said it's legal for him to search my car. He's a policeman, so he must be telling the truth."
Appeal to Ignorance
When a claim is considered true because it hasn't been disproven (or vice versa). Examples:
"Since you cannot prove that Aliens do not exist, then they must exist."
"John said he saw a UFO last night, but he didn't get a photo. He must be lying."
When a concept is considered true because lots of people believe it's true.
"9 out of 10 doctors agree that Medicine X is the best. So then Medicine X must be the best."
"This TV show is the best show on TV right now. Everyone is watching it!"
Begging the Question
When the statement is assumed true based on the statement itself.
"The Bible is the word of God, because it says so in the Bible."
"How do I know he's stupid? Because he doesn't know anything about anything."
"Marijuana wouldn't be illegal if it wasn't seriously harmful to your health."
When a question contains the presumption of guilt.
"So when exactly did you stop hitting your wife?" (Assumes the person WAS hitting his wife).
"Being that spanking children is a good parenting technique, should it be allowed in the United States?"
When a statement's conclusion does not follow from its premise.
"If you don't buy this type of food, then you are neglecting your children's health."
"I hear loud shouting and rustling noises through the wall. The man next door must be hitting his wife."
When someone diverts the attention away from the topic to a NEW topic to throw you off and win the argument.
Topic A is being debated.
Topic B is introduced as being related to Topic A.
Topic A is abandoned.
Now Topic B is being used to discredit you.
"So you think abortion results in lower crime rates. Well, we've all see what happened in Nevada with that abortion doctor who killed his patients with dirty equipment. You want that? You want to see patients killed in dirty clinics? Then go ahead and support abortion."
When it's assumed that a small step leads to a larger chain reaction of events resulting in a greater impact.
"Once the government has passed this gun law, they'll pass other gun laws resulting in total confiscation."
"If we legalize abortion, then next thing you know we'll be killing new born babies."
When someone ignores the argument and replaces it with a distorted or exaggerated version of that argument.
Person A: "Evolution states that humans developed over a long time from the same common ancestor as the gorilla."
Person B: "Everyone listen to Person A. He's saying that we decended from baboons!!!"