3.4: Inductive and Deductive Reasoning
- Page ID
- 89966
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- Identify and utilize deductive and inductive reasoning
Ask somebody who has a job as to why they have a job and there is a good chance they have a reason or multiple reasons. Most likely they will respond by saying that they need the money for their basic necessities. They may even respond that they just want to keep busy or that their parents told them they had to. The point is that there are reasons.
Reasoning is the act of drawing a conclusion from assumed fact(s) called premise(s).
Identify the premise(s) and conclusion in each case of reasoning:
a) "Martha wants to buy a new smartphone, so she decides to get a job."
b) The traffic app notifies Pedro that the traffic on Interstate 215 North will cause him to arrive at his destination at 3 p.m., an hour later than he expected. The app also shows that Interstate 15 North will allow him to arrive at his destination at 2:30 p.m. Pedro decides to take the Interstate 15 North.
Solutions
a) The premise is that Martha wants to buy a new smartphone and the conclusion is that she decides to get a job.
b) There are two premises in this example. One, that the traffic on Interstate 215 North will cause Pedro to arrive at his destination at 3 p.m, and the other that Interstate 15 North will allow him to arrive at his destination at 2:30 p.m. The conclusion is that Pedro takes the Interstate 15 North.
There are many different forms of reasoning defined by scholars, two of which are defined below.
Inductive reasoning: uses a collection of specific instances as premises and uses them to propose a general conclusion.
Deductive reasoning: uses a collection of general statements as premises and uses them to propose a specific conclusion.
Notice carefully how both forms of reasoning have both premises and a conclusion. The important difference between these two types is the nature of the premises and conclusion. Applying these definitions to some examples should illuminate the differences and similarities.
Identify the premises and conclusion of the reasoning below. Identify the type of reasoning used and explain your choice.
a) “When I went to the store last week I forgot my purse, and when I went today I forgot my purse. I always forget my purse when I go to the store”
b) “Every day for the past year, a plane flies over my house at 2 p.m. A plane will fly over my house every day at 2 p.m.”
c) "All electronic devices are useful. My cell phone is an electronic device. Therefore, my cell phone is useful."
d) Spicy food makes me teary. Habanero sauce is spicy food. Habanero sauce makes me teary.
Solution
a) The premises are:
- When I went to the store last week I forgot my purse.
- When I went today I forgot my purse.
The conclusion is:
- I always forget my purse when I go to the store
This is an example of inductive reasoning because the premises are specific instances, while the conclusion is general.
b) The premise is:
- Every day for the past year, a plane flies over my house at 2 p.m
The conclusion is:
- A plane will fly over my house every day at 2 p.m.
This is an example of inductive reasoning because the premises are specific instances, while the conclusion is general.
c) The premises are:
- All electronic devices are useful.
- My cell phone is an electronic device.
The conclusion is:
- My cell phone is useful.
d) The premises are:
- Spicy food makes me teary.
- Habanero sauce is spicy food.
The conclusion is:
- Habanero sauce makes me teary.
This is an example of deductive reasoning because the premises are general statements, while the conclusion is specific.