By Stephanie Gibbons and Justine Kingsbury, adapted by Marc Chao and Muhamad Alif Bin Ibrahim

We have previously discussed how to evaluate the structure of an argument, which involves examining the connection between the premises and the conclusion. The terms used to describe the structure of arguments are valid and invalid (for deductive arguments) and strong (for non-deductive arguments).

However, a good argument requires more than just validity or strength. A valid or strong argument might have premises that are false, and in such cases, the conclusion should not be accepted based on those premises, despite the argument’s validity or strength. A good argument must also have true premises. When evaluating whether an argument is persuasive, consider whether it is sound (for deductive arguments) or cogent (for non-deductive arguments).

Some definitions:

• A sound argument is valid and has all true premises.
• A cogent argument is strong and has all true premises.

We will now discuss how to assess the truth of an argument’s premises.

Remember: for an argument to be sound, it must be both valid and have true premises.

We already know how to assess the validity or strength of an argument. To determine whether an argument is sound or cogent, we must evaluate the truth of its premises.

People often hesitate to determine the truth value of a statement, saying things like “it’s just an opinion” or “there isn’t really one truth”. However, assessing the truth of statements is essential in argument evaluation, and it is important to make an effort to do so.

Is There Such a Thing as Truth?

A statement is true if it accurately describes the world and false if it does not. This common-sense account of truth will be used in this book.

Some statements are uncontroversially true, such as:

• Squares have four sides.

Others are straightforwardly false, like:

• Squares have three sides.

Regardless of how forcefully someone asserts the latter, it remains false.

Some statements are true at certain times and false at others. This variability does not negate their truth or falsity but reflects changes in the world. For example:

• Joe Biden is the President of the United States.

At the time of writing, this statement is true. At some time in the future, it will be false. This temporal aspect does not affect the statement’s current truth.

The truth of claims can change, affecting the soundness or cogency of arguments. For instance:

This argument is sound as long as Joe Biden is President. When he is no longer President, the argument will cease to be sound.

Some statements are obviously true, while others require investigation to establish their truth or falsity.

If you needed to look up the answer to the question, that is acceptable. You are not expected to know everything already.

Sometimes, assessing the truth of a statement is challenging. For example:

• It is raining.

This statement might be true now but false tomorrow, or true in one location but not another. The difficulty lies in the statement’s specificity. Generally, when someone says “It is raining”, they mean “It is raining here, at the moment”. Making statements more specific by including time and place references can help, but it is often unnecessary.

In some cases, it is impossible to determine the truth or falsity of a statement, even after research. When this happens, you may need to suspend judgement on the statement’s truth and the argument’s soundness or cogency. However, do not give up too soon when assessing truth. If you find yourself frequently saying “who really knows?” you may be giving up prematurely.

Scepticism is a philosophical position that involves doubting the truth of nearly everything. Even sceptics live their lives as if many ordinary claims are true. While you may adopt scepticism, it is important to take a more practical approach to truth when assessing everyday arguments.

Some propositions are more difficult to assess than others. It is important not to give up but to pause and think carefully.

Consider the statement:

• Most of the people reading this textbook are enrolled in a course.

Is this true?

To evaluate its truth, note that most people in the world are not enrolled in any course. If the statement is true, it must be specific to people who read this textbook. Not all readers are enrolled in a course, but many are, especially if the textbook is assigned for a course. The likelihood of the textbook being a bestseller read for fun is low. Therefore, it is reasonable to conclude that most readers are enrolled in a course.

Determining truth is not always easy, but it is possible and important.

Cogent Arguments and False Conclusions

In a deductively valid argument, the truth of the premises guarantees the truth of the conclusion. This means that a valid argument with true premises must have a true conclusion, making sound arguments particularly useful.

In non-deductive arguments, the relationship between the premises and the conclusion is different. In a strong argument, the truth of the premises makes the conclusion likely but does not guarantee it. Consequently, it is possible to have a cogent argument with a false conclusion.

Consider the following argument:

This is a strong argument: the truth of the premise does not guarantee the truth of the conclusion, but it does make it very likely. There is no issue with the form of the argument.

The premise is true (there have been 46 US presidents, and 45 of them have been white men.)

Since we have a strong argument with true premises, this argument is cogent.

However, note that the 44th president of the United States was Barack Obama, who is not a white man. Thus, this is a cogent argument with a false conclusion.

We can make this even more explicit:

This argument remains cogent.

This is a consequence of the way cogency is defined. Any strong argument with true premises will be cogent, even if the conclusion is false.

This implies an additional step when assessing cogent arguments compared to sound arguments. In a sound argument, the truth of the conclusion is guaranteed and does not need to be independently assessed. In a cogent argument, once the argument has been established as cogent, it is prudent to consider whether there is any additional reason to believe the conclusion is false. While uncommon, there may be additional information that indicates the conclusion is false. This does not negate the cogency of the argument (as cogency is determined by its definition), but it is a relevant consideration in the assessment of cogent arguments.