How to Evaluate Reasoning

There are quite a few books, movies and television programs where children see their parents as either being completely naive or possibly a space alien from another planet.

Today we will grapple with this question as we examine the concept of evaluating reasoning.

Join me as we pull off the covers of typical parental advice to evaluate the reasoning behind some of their biggest and most universal quotes!

Let’s say our fictional parents like to extend their advice by placing notes in the lunchboxes of their two children.

Little Johnny pulls out the note in his lunchbox today and it’s from his mom.

His note reads ‘Always wear clean underwear; you might be in an accident and the doctors will think you are a dirty person.

Little Johnny looks at this note in horror - that’s it; his mom must be from Mars (or more likely Pluto) with this type of advice.

Hold on, Little Johnny; before we can label Mom a space alien, let’s use an evaluation of reason to determine whether or not this is good advice.

So what are the steps Little Johnny can use to see if Mom is being reasonable with her advice?

Or has she confused this world with the one she left on Neptune?

The first thing Little Johnny must do is break down the claim.

A claim has two parts, the conclusion and the premise.

The conclusion is the claim that is given as a reason for believing.

The premise is the argument given to support the claim.

For Little Johnny, his mother’s conclusion is that you should always wear clean underwear.

The premise, or reason, for wearing clean underwear is that you might be in an accident and the doctors will think you are a dirty person.

So we have our first two steps laid out for us: number one, identify the conclusion, and step two, identify the stated premise.

When checking the premise, be aware that there can be more than one premise for a conclusion.

You will want to evaluate each premise when deciding if the conclusion is true or false.

Well, this one seems a bit straightforward for our character.

Little Johnny understands that when looking for underwear in the morning, he should pull it out of his drawer where everything has been washed and folded rather than pull a pair out of the dirty clothes hamper.

But why the fuss about clean underwear?

However, there might be something amiss in this letter.

Little Johnny has to stop and think just a little bit more before moving forward.

Is there something else hidden between the lines of this claim?

Little Johnny needs to also look for any unstated premise.

For instance, is there anything not stated that needs to be true in order for the premise to lead to the conclusion?

Little Johnny needs to proceed to the next step: number three, identify any implied or unstated premise.

An implied or unstated premise is a premise that isn’t specifically written out but can be reasonably implied to make the stated principle viable.

Our implied or unstated premise in the letter from Johnny’s mom might be that clean underwear actually stays clean following an accident.

Hmmm.

We will let Little Johnny come to his own conclusion on this one!

Now Little Johnny is ready to move on to the meat of evaluating reason - step four: evaluate whether the premise provides reasonable support for the conclusion.

There are two routes normally taken in this evaluation, inductive and deductive validity.

Inductive validity asks us to come up with a reasonable answer from the premise given and evaluate if this is in line with our conclusion.

Put another way, it is improbable for a premise to be true and the conclusion to be false.

However, it is possible, just unlikely, that with the true premise, the conclusion is false.

So inductive validity requires our best guess as to what is likely the outcome from our premise, leading to our conclusion.

Here is an example.

Premise: the Earth has been revolving around the sun for millions of years.

Conclusion: the Earth will revolve around the sun tomorrow.

From the information given, we can reasonably induce that what has been consistent for millions of years will continue to be consistent tomorrow.

However, there is a chance, no matter how small, that the Earth will get upset with the sun and choose to flee to another galaxy for a more stable relationship with a more gentle, caring, loving star.

There isn’t a huge chance that this is going to happen, but we can’t completely rule it out, right?

Deductive validity states that it is impossible for the conclusion to be true if the premise is false.

In other words, if the premise cannot stand on its own, the conclusion has no chance of being true.

In Little Johnny’s case, if one’s underwear cannot stay clean following an accident, it cannot be true the doctors would assume Little Johnny’s soiled pants are from his overall hygiene as opposed to being mauled by a lion on the way to school.

Little Johnny might begin by searching the Internet or looking for journal articles that discuss the cleanliness of underwear following traumatic events that lead to a hospital stay - like kids fainting when their friends prank them by dressing up as a big angry bear and chasing them down the street.

Little Johnny can examine events he has experienced or observed.

Finally, Little Johnny must decide if the premise is correct - number five, evaluate if the premise is true or false.

Be sure to back up your conclusion using data you derived from deductive reasoning or an explanation of the approach you utilized with inductive reasoning.

Little Johnny will need to be able to explain how he came to his final conclusion.

If the premise is true and a good predictor of the stated conclusion, Little Johnny can accept the conclusion.

If our premise is false, Little Johnny must reject the conclusion.

If our premise is true but not a good predictor of the conclusion, Little Johnny again must reject the conclusion under the premise.

The conclusion might be true, but there is no premise by which we can test it within the argument presented, thus the need to reject.

Oftentimes we will read information where we need to evaluate the reasoning behind it.

We do that by looking at the argument presented and finding both the conclusion and the stated premise as well as any implied premise.

We evaluate the premise using a combination of inductive and deductive validity testing or reasoning.

Finally, we evaluate whether or not the premise is true based on our reasoned research.

If the premise is true and a good predictor of the stated conclusion, we can accept the conclusion.

If our premise is false, we must reject the conclusion.

If our premise is true but not a good predictor of the conclusion, again we must reject the conclusion under the premise.

Let us wish Little Johnny good luck.