# Only True Geniuses Can Pass This Deduction Test. Can You?

By: Becky
3 min
Image: shutterstock

Even if you're not Sherlock Holmes, you probably have one or two deductive bones in your body. We know that not everyone will be able to figure out every statement on this quiz. Are you game?

Most deductive arguments follow the classic reasoning pattern of if A = B and B = C, then A = C. But, just because a statement has these three components does not make it correct. To ensure that the deduction (C) is correct, the arguments (A and B) must also be correct. Consider this argument: All presidents live in the White House. George Washington was a president. Therefore, George Washington lived in the White House. Now, we know that, in fact, George Washington, as president, did not live in the White House because construction was not completed on the presidential residence until November 1800. The first statement in this argument, "All presidents live in the White House," is false. If one of the statements is false (even though the second argument, "George Washington was a president," is true), then the deduction must also be false. If course, this requires a bit of knowledge, because if you didn't know that Washington did not live in the White House, you might assume that this deduction was valid.

Are you a genius? Prove it by acing this quiz.

Since all people are mortal, and I am a person, then I am mortal.
valid
invalid

This deduction is valid. From the argument, we can deduce that anyone who is a person is mortal.

All monkeys are mammals and all mammals have kidneys; therefore all monkeys have kidneys.
valid
invalid

This deduction is valid. From the argument, we can deduce that because monkeys are mammals, they have kidneys.

Be careful around bees, they might sting you. All bees will sting you.
valid
invalid

This deduction is invalid. To be valid, an argument must follow the classic reasoning pattern of if A = B and B = C, then A = C. This argument does not do so.

Since all squares are rectangles, and all rectangles have four sides, all squares have four sides.
valid
invalid

This deduction is valid. From the argument, we can deduce that because squares are rectangles, they must have four sides.

If Nancy misses work today and at work today there is a party, then Nancy will miss the party.
valid
invalid

This deduction is valid. If the party is at work today, and Nancy does not go to work today, we can deduce that Nancy will miss the party.

Anyone who lives in the city of Cleveland also lives in Ohio. Ed lives in Ohio; therefore, he lives in Cleveland.
valid
invalid

This deduction is not valid. There are other cities in Ohio, which makes this argument false.

All crows are black. My cat is black. Therefore my cat is a crow.
valid
invalid

This deduction is not valid. The argument does not say that everything black is a crow.

All numbers ending in 0 or 5 are divisible by 5. The number 35 ends with a 5, so it is divisible by 5.
valid
invalid

This deduction is valid. ALL numbers that end in 0 or 5 are divisible by 5.

All birds have feathers and eagles are birds, so eagles have feathers.
valid
invalid

This argument is valid. It is correct to deduce that any bird has feathers.

It is dangerous to drive on icy streets. The streets are icy now, so it is dangerous to drive now.
valid
invalid

This deduction is valid. If the argument is true, then the deduction is true.

All dogs have a keen sense of smell. Fido is a dog, so Fido has a keen sense of smell.
valid
invalid

This deduction is valid. If Fido is a dog, then, according to the argument, Fido must have a keen sense of smell.

All dogs growl. Be careful of growling dogs, or you will get bitten.
valid
invalid

This deduction is not valid. If the argument said "all growling dogs bite," then it might be valid.

Snakes are reptiles, and all reptiles are cold-blooded; therefore, snakes are cold-blooded.
valid
invalid

This deduction is valid. If all reptiles are cold-blooded, and all snakes are reptiles, then it stands to reason that snakes are cold-blooded.

If all plants perform photosynthesis, and trees are plants, then trees perform photosynthesis.
valid
invalid

This deduction is valid. From the argument, we can assume that trees perform photosynthesis.

All red meat contains iron. Beef is red meat, so beef contains iron.
valid
invalid

This deduction is valid. If all red meat contains iron, then it follows that, if beef is red meat, beef contains iron.

Some cats are grey. Fluffy is a cat, therefore she is grey.
valid
invalid

This deduction is not valid. The argument does not say that ALL cats are grey.

China has never had a queen. Lilly wants to be queen of China, but she can't.
valid
invalid

This deduction is invalid. To be valid, an argument must follow the classic reasoning pattern of if A = B and B = C, then A = C. This argument does not do so.

All acute angles are less than 90 degrees. If an angle is 40 degrees, it must be acute.
valid
invalid

This deduction is valid. From the argument, we can deduce that a 40-degree angle must be acute.

All noble gases are stable, and helium is a noble gas, therefore helium is stable.
valid
invalid

This deduction is valid. If helium is a noble gas, it must be stable.

Lions have cells in their bodies and all cells have DNA, so lions have DNA.
valid
invalid

This deduction is valid. If all cells have DNA, and lions have cells, then lions must have DNA.

All cars have at least two doors. Chevys are cars. Therefore, all Chevys have at least two doors.
valid
invalid

This deduction is valid. From the argument, we can deduce that all Chevys have at least two doors.

Candy's new boyfriend drives an old car. He must be poor. Candy should break up with him.
valid
invalid

This deduction is invalid. The boyfriend might be frugal, not poor, and he might be a great guy.

All Dubliners are from Ireland. Betty is not a Dubliner, therefore, Betty is not Irish.
valid
invalid

This deduction is not valid. There are other cities in Ireland.

I saw a robin, and then I crashed my car. Robins are bad luck.
valid
invalid

This deduction is not valid. Cause and effect does not necessarily lead to logical deductions.

Hospitals are full of sick people. Therefore, hospitals make people sick.
valid
invalid

This deduction is not valid. In this case, hospitals are full of sick people, because sick people go there.

All ducks have bills. The Mallard is a duck; therefore, the Mallard has a bill.
valid
invalid

This deduction is valid. Both arguments are true, leading to a valid deduction.

The apple hit me on the head. Apples fall because of gravity. All apples will hit you on the head.
valid
invalid

This deduction is invalid. Although both arguments may, in fact, be true, they do not lead to a valid deduction.

If we let your sister stay, we will have to let your whole family stay.
valid
invalid

This deduction is invalid. To be valid, an argument must follow the classic reasoning pattern of if A = B and B = C, then A = C. This argument does not do so.

All horses have manes and the Palomino is a horse; therefore, Palominos have manes.
valid
invalid

This deduction is valid. If we assume that both arguments are correct, then it follows that the deduction is also correct.

Everyone in my family is named Jones. I am a member of my family, therefore I must also be named Jones.
valid
invalid

This deduction is valid. It follows that, if both arguments are correct, the deduction must also be correct.

All dogs have four legs. A corgi is a dog, therefore corgis have four legs.
valid
invalid

This deduction is valid. If all dogs have four legs, and a corgi is a dog, then it follows that corgis must have four legs.

All apples are red. Oranges are a fruit. Therefore, oranges must be red.
valid
invalid

This deduction is invalid. Although both arguments are correct, they are unrelated, so the deduction is incorrect.

All cats can meow. My cat is black. Therefore my cat can meow.
valid
invalid

This deduction is invalid. Although the arguments and the deduction statement are all correct, the arguments are unrelated.

All fish can swim. A shark is a fish. Therefore, a shark can swim.
valid
invalid

This deduction is valid. If a shark is a fish, then we may assume that sharks can swim.

All cars use fuel. My Ford is a car. Therefore, my Ford uses fuel.
valid
invalid