Deductive reasoning is from general to specific. It is very important that the initial premise is correct. If it’s wrong, the conclusion will be false too. Just because an argument is valid, it doesn't follow that the conclusion is true. The conclusion is from the first premise. Example: ISE teachers are kind. Mr. Overacker is an ISE teacher, therefore Mr. Overacker is kind. It is not informative because it doesn’t have any investigation or any more observation about Mr. Overacker. Deductive reasoning is certain, but it isn’t necessary need to be true to be certain, so this is its weakness. Logic is most useful when we begin with true premises; for if we then reason validly we can be sure that the conclusion is true. If people use deductive reasoning and follow every step correctly, the conclusion could be true or not true. It depends on the first premise. Your conclusions are only as good as your premises.
Informal reasoning is the fallacies of both deductive and inductive reasoning. Fallacies are false ideas or beliefs, especially ones that a lot of people believe are true. This is very common in every day life. Informal reasoning is a normal logic, people use in regular argument. For example: This Thai restaurant is bad because the cook is Indian. People claim that something is true on the grounds that there is no evidence to disprove it. It means that the Thai food doesn’t taste good because the cook is not Thai and there is no evidence to prove that this is wrong. This is ad hominem fallacy. It consists in attacking or supporting the person rather than the argument. All of the bad reasoning can cause by the confirmation bias, discrimination, prejudice, and generalization. Also generalization help you survive. For example: if the food smells good, look right, we just eat it. We won’t go through detail about what it’s made off. Even though informal reasoning doesn’t have a lot of evidence and something the language can be ambiguous, it is also help you to survive. The equivocation can use language ambiguously. For example: A hamburger is better than nothing. Nothing is better than good health. Therefore a hamburger is better than good health. If you were worrying about good health, you won’t eat hamburger, but if there is nothing else to eat and people say this, you will change your mind and eat hamburger to survive. Circular reasoning assumes the truth of what you are supposed to be proving. People just keep asking questions. For example “three thieves are arguing about how to divide up the seven pearls they have stolen. One of them picks up the pearls and gives two to each of the other two, keeping the remaining three for himself. One of the other men says ‘How come you have kept three?’ ‘Because I am the leader.’ ‘Oh. But how come you are the leader?’ ‘Because I have more pearls.’” It’s keep proving.
All reasoning has weaknesses and strengths. Deductive, inductive and informal reasoning all have weakness and strength to some extent. Deductive is more certain, but it is less informative. Even though it can have weakness, people use it in their daily life. Inductive reasoning is also very helpful, it based on the investigation or observation, but the observation is only with some people and they decide to use it for all people, so they can be mistake. Deductive reasoning also needs inductive reasoning because the first premise in deductive reasoning is from inductive reasoning. Informal reasoning is fallacy. It is also called false reasoning. It is a false idea that everyone believes is true. If everyone prejudice on some nationality, they will think that everyone from that nationality is bad. Sometimes people believe something is true because they can’t prove to be false.
