Deductive reasoning is based on premises and if the premises are true, then the reasoning will be valid.
Deductive Reasoning: Everyday Examples
- In mathematics, If A = B and B = C, then A = C.
- Since all humans are mortal, and I am a human, then I am mortal.
- All dolphins are mammals, all mammals have kidneys; therefore all dolphins have kidneys.
- Since all squares are rectangles, and all rectangles have four sides, so all squares have four sides.
- If Dennis misses work and at work there is a party, then Dennis will miss the party.
- All numbers ending in 0 or 5 are divisible by 5. The number 35 ends with a 5, so it is divisible by 5.
- To earn a master’s degree, a student must have 32 credits. Tim has 40 credits, so Tim will earn a master’s degree.
- All birds have feathers and robins are birds, so robins have feathers.
- It is dangerous to drive on icy streets. The streets are icy now so it is dangerous to drive now.
- All cats have a keen sense of smell. Fluffy is a cat, so Fluffy has a keen sense of smell.
- Snakes are reptiles and reptiles are cold-blooded; therefore, snakes are cold-blooded.
- Cacti are plants and all plants perform photosynthesis; therefore, cacti perform photosynthesis.
- Red meat has iron in it and beef is red meat, so beef has iron in it.
- Acute angles are less than 90 degrees and this angle is 40 degrees so this angle is acute.
- All noble gases are stable and helium is a noble gas, so helium is stable.
- Magnolias are dicots and dicots have two embryonic leaves; therefore magnolias have two embryonic leaves.
- Elephants have cells in their bodies and all cells have DNA, so elephants have DNA.
- All cars have at least two doors and a Ford Focus is a car, so the Ford Focus has at least two doors.
- All horses have manes and the Arabian is a horse; therefore Arabians have manes.
Other Patterns of Deductive Reasoning
Some deductive reasoning does not follow the classic reasoning pattern of A = B and B = C, then A = C. Some examples of other patterns are:
- Be careful around bees, they might sting you. (The reasoning is understood that all bees might sting.)
- It takes me an hour to get to the mall. If I leave at five o’clock I will reach the mall by six o’clock.
- That dog is growling so be careful or you might get bitten. (It is logical is the dog is angry, he might bite.)
- The apple hit me on the head because of gravity.
- There are three people in my family. Each one is tall, so everyone in my family is tall.
You can use deductive reasoning to better understand the world around you.
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