Arguments: Good, Bad and Weird

Deductive arguments...

• can be said to be valid or invalid, or sound/unsound

• can be said to be weak or strong.

A sound argument is a valid argument with true premises

• True

• False

Inductive arguments...

• Are outside-in: start general and then get specific

• Are inside-out: start specific and then get general

Inductive arguments...

• can be strong or weak

• can be valid or invalid

Answer explanation

Deductive reasoning can be valid or invalid

Inductive reasoning involves using patterns to come up with broader generalizations

• True

• False

Inductive arguments have premises that can offer a likely conclusion

• True

• False

All bachelors are unmarried men. John is an unmarried man. Therefore, John is a bachelor.

• This is an inductive argument.

• This is a deductive argument.

Answer explanation

This example illustrates deductive reasoning by starting with a general premise, ‘all bachelors are unmarried men,’ and then shrinking the statement to apply to the particular or specific instance.

In this case: John is a man, and he is not married; therefore, John is a bachelor. The conclusion is indisputable, unlike in inductive reasoning, where the conclusions are just educated guesses.

For five years in a row, I have seen bears in the woods in June but not May. This year, I expect to wait until June to see a bear in the woods.

• This is a valid deductive argument.

• This is a weak inductive argument.

• This is a strong inductive argument.

• This is an invalid deductive argument.

Answer explanation

In this example, a person who lives near the woods has identified a seasonal trend that allows them to generalize and predict future patterns. This sort of seasonal prediction has been around for millennia. Agriculturalists use seasonal trends to reason about when to plant their seeds. This doesn’t mean every year will be perfect (to this day, some seasons are terrible for crop yield).

Anyone born in late August to late September is a Virgo. Ashley was born on September 4th. Therefore, Ashley is a Virgo.

• This is an inductive argument.

• This is a deductive argument.

Answer explanation

While deductive logic goes from the top-down, based on the set of premises given in this example it’s clear that we could induce (or build-up,) to the correct conclusion as well.

Bottom-up reasoning, or arriving at a broad conclusion based on specific premises is known as inductive reasoning, and is in contrast to deductive reasoning.

All my siblings are left-handed, and we are all talented artists. People that are left-handed are more creative and artistically inclined than those that are right-handed.

• This is a weak inductive argument.

• This is a weak deductive argument.

• This is a sound inductive argument.

• This is an invalid deductive argument.

Answer explanation

It could seem reasonable for this person to assume (based on the evidence that they are exposed to) that left-handed people are naturally more creative and artistic than their right-handed counterparts. Despite appearances, it is not proven that left-handed people are in fact more artistic than right-handed people.

The misstep in logic occurs from making the move from the specific to the general without having sufficient evidence to substantiate the claim as a generally applicable rule.